Running a retail store, restaurant, salon, café, or service business requires more than simply accepting payments. Businesses need to manage products, inventory, customers, employees, receipts, taxes, discounts, refunds, and sales reports from one system.
A Point of Sale (POS) platform brings these operations together.
Square is a well-known example. Its POS ecosystem combines checkout and payment acceptance with business-management capabilities, while its developer platform exposes APIs for orders, catalog, inventory, customers, staff, and payments. (Square)
Building a POS system like Square does not mean recreating its entire financial infrastructure. A practical approach is to build the POS software first and integrate regulated payment providers and compatible hardware for payment processing.
In this guide, we will cover the architecture, essential features, technology stack, database, inventory, checkout, payments, offline mode, reporting, and security required to build a modern POS platform.
1. What Is a POS System?
A POS system is the software and hardware businesses use to complete sales and manage related store operations.
Traditional POS systems mainly worked as digital cash registers.
Modern POS platforms can manage much more:
- Product catalog
- Shopping cart
- Cash and digital payments
- Inventory
- Orders
- Customers
- Employees
- Discounts
- Taxes
- Refunds
- Receipts
- Multiple stores
- Sales reports
- Hardware devices
A typical setup might include:
POS Application
↓
Product Catalog
↓
Shopping Cart
↓
Checkout
↓
Payment
↓
Receipt
↓
Inventory Update
↓
Sales ReportSquare similarly describes modern POS systems as combining a checkout device, payment processing, POS software, and optional hardware such as barcode scanners, receipt printers, and cash drawers. (Square)
2. How Does a POS System Like Square Work?
Suppose a customer enters a retail store and purchases two products.
The cashier opens the POS application and scans the products.
The POS retrieves product information:
Product A
₹500
Product B
₹1,000The cart calculates:
Subtotal: ₹1,500
Discount: ₹100
Tax: ₹252
Total: ₹1,652The customer selects a payment method.
After payment is confirmed, the system completes the order, updates inventory, generates a receipt, records the transaction, and updates reports.
Example: A modern POS interface combining product selection, cart management, and checkout.
The important point is that an order should connect multiple parts of the platform instead of simply recording a payment.
Square’s Orders API follows a similar connected model: orders can contain line items, taxes, discounts, fulfillment information, and payment information, while catalog-based sales can update inventory. (Square)
3. Decide What Type of POS You Want to Build
Do not start development before choosing your target industry.
Different businesses need different POS workflows.
Retail POS
Suitable for:
- Clothing stores
- Grocery stores
- Electronics shops
- Pharmacies
- General retail
Important features include barcode scanning, inventory, variants, returns, suppliers, and multiple locations.
Restaurant POS
Restaurants may require:
- Menu management
- Table management
- Kitchen orders
- Modifiers
- Split bills
- Tips
- Kitchen display systems
- Takeaway orders
Salon and Service POS
A salon may need:
- Appointment booking
- Staff management
- Services
- Customer history
- Memberships
- Payments
Mobile POS
Mobile POS applications allow businesses to complete transactions using phones or tablets.
For an MVP, choose one industry instead of trying to support every business type.
4. Build the Product Catalog
The product catalog is one of the foundations of your POS.
Each product can contain:
Product Name
SKU
Barcode
Category
Selling Price
Cost Price
Tax
Stock
Image
Description
StatusYou should also support product variations.
For example:
Nike T-Shirt
↓
Small / Black
Medium / Black
Large / Black
Medium / WhiteEach variation can have its own:
SKU
Barcode
Price
InventorySquare’s current Catalog API uses a similar distinction between catalog items and item variations and also supports categories, discounts, taxes, options, and pricing rules. (Square)
This structure is especially useful for fashion and retail businesses.
5. Add Categories and Product Search
Cashiers must be able to find products quickly.
Create categories such as:
Clothing
Electronics
Food
Beverages
AccessoriesThe POS interface should support:
- Product search
- Category filters
- SKU search
- Barcode search
- Favorites
- Recently used products
Speed matters.
A cashier should not need to navigate through multiple screens simply to add an item.
For stores containing thousands of products, use local caching and efficient database search.
6. Build Barcode Scanning
Barcode scanning can significantly improve retail checkout speed.
A typical workflow is:
Scan Barcode
↓
Find Product
↓
Retrieve Price
↓
Check Product Status
↓
Add to CartYou can support a hardware barcode scanner or use the device camera where appropriate.
For example:
Barcode:
8901234567890
↓
Product:
Premium Coffee
Price:
₹450If the same barcode is scanned again, you can increase the cart quantity instead of creating an unnecessary duplicate row.
For weighted products and specialized retail workflows, barcode handling may require additional logic.
7. Build the Shopping Cart
The cart should remain fast even when the store has unreliable internet connectivity.
Each cart item can contain:
Product
Variation
Quantity
Unit Price
Discount
Tax
TotalAllow the cashier to:
- Increase quantity
- Decrease quantity
- Remove products
- Add notes
- Apply eligible discounts
- Select customers
- Hold the cart
- Resume held orders
A held-cart feature is useful when one customer temporarily leaves checkout and the cashier needs to serve another customer.
8. Implement Taxes and Discounts
POS systems often need flexible tax and discount rules.
Discounts
Support:
10% discount
₹500 fixed discount
Buy 2 Get 1
Employee discount
Promotional discountDiscounts may apply to individual products or the entire eligible order.
Taxes
Products may have different tax rules depending on the business and jurisdiction.
Therefore, store tax configuration separately instead of hardcoding a single percentage.
Your calculation engine should have a clearly defined order for:
Price
↓
Discount
↓
Taxable Amount
↓
Tax
↓
Final TotalThe exact calculation depends on whether prices are tax-inclusive or tax-exclusive and on applicable tax requirements.
Square’s order model also supports taxes and discounts at the order and line-item level. (Square)
9. Choose the Right Technology Stack
A modern POS usually needs applications that can work reliably on store devices while synchronizing data with a backend.
Flutter – POS Application
Flutter is a strong option for developing tablet, Android, iOS, and supported desktop POS interfaces from a shared codebase.
You can build:
Checkout
Product catalog
Barcode scanning
Orders
Customers
Inventory
Reports
Employee loginA local database can also support offline workflows.
Next.js – Admin Dashboard
Use Next.js for the browser-based business dashboard.
Store owners can manage:
Products
Inventory
Employees
Stores
Orders
Customers
Reports
SettingsNode.js + NestJS – Backend
The backend can manage:
Authentication
Products
Orders
Inventory
Customers
Stores
Employees
Payments
Reports
SynchronizationNestJS can help keep a growing backend modular.
PostgreSQL – Central Database
Use PostgreSQL for:
Businesses
Locations
Products
Orders
Customers
Inventory
Employees
PaymentsSQLite – Local POS Database
SQLite can store essential information directly on the POS device.
This becomes especially useful for offline mode.
Redis
Redis can support caching, rate limiting, and appropriate coordination tasks.
However, permanent sales and financial records should remain in your authoritative database.
10. Design the POS Database
Your database should reflect the relationships between stores, products, orders, and inventory.
A simplified structure could contain:
Businesses
business_id
name
currency
timezone
tax_settingsLocations
location_id
business_id
name
addressProducts
product_id
business_id
name
category_id
statusProduct Variants
variant_id
product_id
sku
barcode
priceInventory
location_id
variant_id
quantityOrders
order_id
location_id
customer_id
employee_id
subtotal
discount
tax
total
statusOrder Items
order_item_id
order_id
variant_id
quantity
unit_price
discount
tax
totalPayments
payment_id
order_id
method
amount
status
provider_referenceKeep order-item prices separate from the current product price.
If a product costs ₹500 today and ₹600 next month, yesterday’s receipt must still show ₹500.
This snapshot-style behavior is also important in Square’s order model, which preserves the relevant order state used for transaction calculations. (Square)
11. Build Order Management
An order should represent the complete sale.
Possible order states include:
Draft
↓
Pending Payment
↓
Paid
↓
CompletedOther states may include:
Cancelled
Partially Refunded
RefundedThe order should store the complete historical transaction.
For example:
Order #POS-10582
2 × T-Shirt ₹1,000
1 × Shoes ₹2,000
Subtotal ₹3,000
Discount ₹300
Tax ₹486
Total ₹3,186Do not rebuild historical orders using today’s product prices.
The order must preserve the values applicable when the transaction occurred.
12. Integrate Payment Processing
A POS can support multiple payment methods.
For example:
Cash
Card
UPI
Digital Wallet
Gift Card
Other supported methodsFor electronic payments, integrate an appropriate regulated payment provider rather than attempting to process raw payment credentials yourself.
A payment flow can look like:
POS
↓
Create Order
↓
Select Payment Method
↓
Payment Provider
↓
Payment Confirmation
↓
Complete OrderNever mark an electronic transaction as successful only because the frontend says the payment succeeded.
Your backend should confirm the result through the payment provider’s supported mechanism.
Square itself offers several ways for developers to connect payment experiences, including POS, mobile, terminal, web, and in-app payment integrations. (Square)
13. Support Cash Payments
Cash still matters for many physical businesses.
The cashier enters:
Total:
₹850
Cash Received:
₹1,000The POS calculates:
Change:
₹150Store both the payment amount and method.
Cash payments should also connect with register sessions so managers can reconcile the expected amount against actual cash.
14. Add Split Payments
Some customers may want to pay using multiple payment methods.
For example:
Order Total
₹5,000
Cash
₹2,000
Card
₹3,000Your database should therefore allow multiple payments against one order.
Conceptually:
Order
↓
Payment 1 – Cash
Payment 2 – CardThe order becomes fully paid only after successful payments cover the required amount according to your business rules.
This architecture also helps with partial payments.
15. Build Inventory Management
Inventory should connect directly with completed sales.
Suppose the store has:
Product:
Wireless Headphones
Available Stock:
25The customer purchases two.
After the sale:
Available Stock:
23However, do not simply overwrite 25 with 23 without maintaining history.
Create an inventory movement:
Type: Sale
Quantity: -2
Order: POS-10582This provides an audit trail.
Square’s Inventory API similarly manages inventory counts and changes, while catalog-based completed orders can update inventory quantities. (Square)
16. Add Inventory Movements
Inventory changes for many reasons besides sales.
Support movement types such as:
Sale
Return
Purchase
Transfer
Damage
Adjustment
Initial StockSuppose an employee manually changes inventory from 50 to 45.
Do not silently replace the quantity.
Record:
Previous Quantity: 50
New Quantity: 45
Adjustment: -5
Reason: Damaged Products
Employee: Store ManagerThis makes inventory problems much easier to investigate.
17. Add Multi-Location Inventory
Businesses with multiple stores need location-level stock.
For example:
iPhone Case
Jaipur Store
20
Delhi Store
35
Warehouse
100Inventory should therefore belong to:
Product Variation + Locationnot only to the product.
This allows businesses to transfer inventory:
Warehouse
-10
↓
Jaipur Store
+10Create linked inventory movements for transfers so stock history remains traceable.
18. Build Customer Management
Allow businesses to optionally attach customers to orders.
A customer profile may contain:
Name
Phone
Email
Address
Purchase History
Total Orders
Total Spend
NotesCustomer history can help businesses understand repeat purchases and provide better service.
Square’s developer platform likewise includes customer APIs alongside payments and commerce capabilities. (Square)
For privacy, collect only customer information the business actually needs and protect access appropriately.
19. Add Loyalty Programs
Once customer profiles are working, you can introduce loyalty features.
For example:
₹100 spent
=
1 loyalty pointA customer spending ₹5,000 earns:
50 PointsPoints might later be redeemed according to merchant-defined rules.
The POS should clearly show:
Current Points
Points Earned
Points Redeemed
Remaining BalanceLoyalty should be connected to customer accounts rather than individual devices.
20. Build Employee Management
Businesses may have multiple cashiers and managers.
Create employee accounts with roles.
For example:
Cashier
Can:
Create sales
Accept payments
View products
Print receiptsSupervisor
Can additionally:
Apply restricted discounts
Approve selected refunds
Manage register sessionsManager
Can:
Manage inventory
View reports
Manage employees
Change store settingsPermissions must be enforced on the backend, not only by hiding frontend buttons.
21. Build Register and Cash Drawer Management
Physical stores often need register sessions.
A cashier starts the shift with:
Opening Cash
₹5,000Throughout the day:
Cash Sales
+₹25,000
Cash Refunds
-₹2,000
Cash Added
+₹1,000
Cash Removed
-₹500At closing, the system calculates the expected cash.
The cashier counts the physical cash and enters the actual amount.
The POS can then show any difference.
This creates stronger accountability for cash operations.
22. Generate Receipts
After a completed sale, generate a receipt.
For example:
ABC Store
Order #10582
24 September 2026
T-Shirt × 2 ₹1,000
Shoes × 1 ₹2,000
Subtotal ₹3,000
Discount ₹300
Tax ₹486
Total ₹3,186
Payment: CardSupport:
- Printed receipt
- Email receipt
- SMS receipt
- Digital receipt
For printed receipts, integrate with compatible thermal printers.
Do not generate historical receipts using current product information if the transaction snapshot contains different names, prices, or tax values.
23. Add Refunds and Returns
Returns are common in retail.
A cashier can search by:
Receipt Number
Order Number
Customer
TransactionThe POS retrieves the original order.
The employee selects the items being returned.
For example:
Original Order
₹3,000
Returned Item
₹1,000
Refund
₹1,000Do not simply change the original sale from ₹3,000 to ₹2,000.
Keep the original transaction and create linked return/refund records.
Inventory can then be increased when appropriate.
For damaged or non-resellable items, the returned quantity may need a different inventory status rather than going directly back into available stock.
24. Build Offline POS Mode
Offline functionality can be extremely important for physical stores.
Internet connectivity should not necessarily make the entire POS unusable.
Store essential data locally:
Products
Prices
Taxes
Inventory snapshot
Employees
Pending ordersA simplified architecture can be:
Cloud Backend
↕
Sync Engine
↕
Local SQLite
↕
POS ApplicationWhen the internet is unavailable, supported local operations can continue according to your business rules.
When connectivity returns, pending changes synchronize with the server.
However, offline electronic payment acceptance is a separate financial and risk problem. It should only be enabled when your payment provider and hardware explicitly support an approved offline flow.
25. Handle Offline Synchronization Conflicts
Offline mode introduces difficult synchronization problems.
Imagine two POS devices both believe the store has one remaining product.
Both devices go offline.
Each device sells the product.
When they reconnect, the server receives two sales.
Your synchronization system needs clear conflict rules.
For inventory, maintain movements instead of trusting a device’s final quantity.
Instead of syncing:
Stock = 0sync:
Sale:
-1 unitThe server can then process the complete inventory history and identify negative-stock situations when necessary.
Use globally unique IDs for offline-created orders so synchronization retries do not create duplicate sales.
26. Add Hardware Integration
A complete POS may need hardware such as:
Barcode Scanner
Receipt Printer
Cash Drawer
Customer Display
Card Reader
POS Terminal
Weighing ScaleCreate a hardware abstraction layer rather than placing device-specific code throughout the application.
For example:
PrinterService
printReceipt()
openCashDrawer()Different printer implementations can then support Bluetooth, USB, LAN, or other available connections.
Payment hardware should use official SDKs or APIs provided by the selected payment provider or device manufacturer.
For example, Square’s Terminal API allows a custom POS application to communicate with Square Terminal for supported in-person payments. (Square)
27. Build the Admin Dashboard
Store owners need a web dashboard for managing the business.
The dashboard can include:
Overview
Today's Sales
Orders
Average Order Value
Refunds
Low StockProducts
Manage products, variants, categories, prices, and barcodes.
Inventory
Manage stock levels, adjustments, transfers, and purchase-related movements.
Orders
View completed, refunded, cancelled, and pending orders.
Customers
View customer profiles and purchase histories.
Employees
Manage staff and permissions.
Locations
Manage stores and warehouses.
Reports
View sales, products, inventory, employee, and tax-related reports.
Keep the main dashboard simple. Detailed analytics should have dedicated screens.
28. Build Sales Reports
Store owners need accurate information about business performance.
Useful reports include:
- Daily sales
- Weekly sales
- Monthly sales
- Sales by product
- Sales by category
- Sales by location
- Sales by employee
- Payment methods
- Discounts
- Taxes
- Refunds
For example:
Today's Sales
Gross Sales ₹1,20,000
Discounts ₹5,000
Refunds ₹3,000
Net Sales ₹1,12,000Clearly define every metric.
Do not mix gross sales, collected payments, taxes, refunds, and net sales into a single number without explaining what it represents.
29. Add Inventory Reports
Inventory reporting can help businesses avoid stockouts and excessive inventory.
Useful reports include:
Current Stock
Low Stock
Out of Stock
Inventory Movements
Stock Adjustments
Transfers
Top-Selling Products
Slow-Moving ProductsYou can also introduce reorder levels.
For example:
Product:
Coffee Beans
Current Stock:
8
Reorder Level:
10The POS alerts the manager that additional inventory may be required.
Later, the platform can connect inventory alerts with supplier and purchase-order functionality.
30. Add Multi-Store Support
A growing business may operate multiple stores.
Your architecture should support:
Business
│
├── Jaipur Store
├── Delhi Store
└── Mumbai StoreEach location can have separate:
Inventory
Employees
Registers
Orders
Taxes
Receipts
Operating settingsOwners can still view consolidated business reports across all locations.
Plan location support early if your target customers include growing retail businesses.
31. Implement Multi-Tenant Architecture
If you plan to sell your POS as SaaS, multiple businesses will share your platform.
For example:
POS SaaS
│
├── Business A
│ ├── Stores
│ ├── Products
│ └── Orders
│
└── Business B
├── Stores
├── Products
└── OrdersBusiness A must never access Business B’s information.
Therefore, every relevant record needs clear tenant ownership.
Your backend should verify:
User
↓
Business
↓
Location
↓
Role
↓
PermissionTenant isolation should be enforced throughout the backend and database design where appropriate.
32. Implement Security
POS platforms handle sensitive business and payment-related information.
Implement:
- HTTPS
- Secure authentication
- Role-based permissions
- Tenant isolation
- Secure API credentials
- Device authentication
- Rate limiting
- Database backups
- Audit logs
- Secure payment integrations
- Monitoring and alerts
Avoid storing sensitive card information yourself.
Use the payment provider’s approved SDK, terminal, reader, tokenization, or hosted infrastructure.
For example, Square states that its POS API delegates supported payment processing and associated hardware handling to Square’s POS infrastructure. (Square)
Your own PCI DSS scope and other obligations still depend on your specific payment architecture.
33. Add Audit Logs
Important actions should be recorded.
For example:
Inventory Adjustment
Product:
Wireless Headphones
Old Quantity:
25
New Quantity:
20
Changed By:
Store Manager
Reason:
Damaged StockAlso record important events such as:
Refund approved
Discount manually applied
Order cancelled
Product price changed
Employee permission changed
Register opened
Register closedAudit logs help businesses investigate mistakes, suspicious activity, and operational problems.
34. Test the Complete POS Workflow
Do not test only individual screens.
Test complete store scenarios.
Normal Sale
Scan Product
↓
Add to Cart
↓
Apply Tax
↓
Accept Payment
↓
Complete Order
↓
Update Inventory
↓
Generate ReceiptAlso test:
- Product out of stock
- Duplicate barcode scan
- Partial refund
- Full refund
- Split payment
- Failed electronic payment
- Payment timeout
- Printer disconnected
- Barcode scanner disconnected
- Internet unavailable
- Offline sale synchronization
- Duplicate synchronization request
- Two stores updating inventory
- Unauthorized refund attempt
- Register cash mismatch
Automated tests are especially valuable for calculations, order states, inventory, and synchronization.
35. How Much Does It Cost to Build a POS System Like Square?
The cost depends heavily on the type of POS and the required hardware integrations.
A small retail POS is much simpler than a complete platform serving retail, restaurants, appointments, e-commerce, payments, and multiple locations.
A practical roadmap can be divided into phases.
Phase 1 – POS MVP
Build:
Products
Categories
Cart
Orders
Cash payments
Basic electronic payment integration
Receipts
Inventory
Employees
Basic reportsPhase 2 – Retail Features
Add:
Barcode scanning
Returns
Refunds
Customers
Loyalty
Stock adjustments
Purchase management
Advanced reportsPhase 3 – Business Features
Introduce:
Multiple stores
Inventory transfers
Offline mode
Advanced employee permissions
Customer management
Hardware integrationsPhase 4 – POS SaaS Platform
Add:
Multi-tenancy
Subscription billing
Business onboarding
Advanced analytics
Third-party integrations
Developer APIs
Industry-specific modulesBuilding in phases allows you to launch faster and validate the system with real businesses before developing every advanced feature.
36. Frequently Asked Questions
Can I build a POS system using Flutter?
Yes.
Flutter is particularly useful for building POS applications that run on tablets and mobile devices from a shared codebase.
You can implement product catalogs, carts, barcode scanning, order management, receipts, offline storage, and hardware integrations where supported.
Can a Flutter POS work offline?
Yes.
You can store products, prices, pending orders, and other essential information locally using a database such as SQLite.
When connectivity returns, the application can synchronize data with the server.
However, offline payment acceptance depends on the capabilities and rules of the payment provider.
Can I integrate a thermal printer with Flutter?
Yes, provided the target printer exposes a compatible connection or SDK.
Depending on the hardware, integrations may use Bluetooth, USB, LAN, manufacturer SDKs, or supported printing protocols.
Always verify hardware compatibility before selecting devices for a production POS.
Can I build a POS without creating my own payment gateway?
Yes.
In fact, this is often the practical approach.
Build the POS, inventory, order, customer, and reporting software while integrating an established payment provider for electronic transactions.
Can I build a POS like Square for Indian businesses?
Yes.
You can build POS software targeted at Indian retailers, restaurants, salons, and other businesses.
The production system should be designed around applicable Indian tax, invoicing, payment, and data requirements for the specific businesses it serves.
How long does it take to build a POS system?
A focused MVP can take several months depending on features, platforms, hardware integrations, offline requirements, and the development team.
A large multi-industry POS ecosystem with payments, inventory, e-commerce, staff management, hardware, and multiple locations is a much larger long-term product.
Conclusion
Building a POS system like Square requires more than creating a checkout screen.
A complete platform needs product management, cart calculations, orders, payments, inventory, customers, employees, receipts, refunds, reports, hardware integration, and reliable synchronization.
Start with a focused POS MVP for one industry.
For example, you can first build a retail POS containing products, barcode scanning, checkout, payments, inventory, receipts, and basic reports.
Once the core transaction flow is reliable, introduce customers, loyalty, multiple stores, offline synchronization, advanced inventory, employee management, and additional hardware integrations.
Most importantly, keep payments, orders, and inventory connected while preserving accurate historical records.
That foundation allows a simple POS application to gradually grow into a complete business-management platform.
Want to Build Your Own POS System Like Square?
Planning to develop a retail POS, restaurant POS, mobile POS, inventory management system, billing application, or complete multi-store business platform?
At Dotcube Technologies, we help businesses design and develop custom web and mobile applications around their operational requirements.
Whether you need a Flutter POS application, barcode scanning, inventory management, payment integration, thermal printer support, customer management, employee permissions, offline functionality, or a complete admin dashboard, the solution can be planned according to your business model.
If you want to build a POS system like Square or a similar retail platform, contact Dotcube Technologies to discuss your project requirements.
Contact Dotcube Technologies:
https://www.dotcubetechnologies.com/#contact
