Overview

Welcome to Westpay PAaS

PAaS, Payment Application as a Service, is Westpay's Android terminal integration model for applications that run on the payment terminal itself. Your app owns the merchant workflow while the Westpay Payment Application handles secure payment processing, card interaction, authorisation, receipts, printer access, and terminal services.

The PAaS library is the bridge between your Android app and the Westpay Payment Application.

How It Works

1. The terminal boots and starts the Westpay Payment Application.
2. The Payment Application performs its secure checks and prepares the terminal.
3. The Payment Application launches your PAaS app.
4. Your app registers with the PAaS library and initialises the terminal.
5. Your app controls the merchant experience until payment is needed.
6. Your app sends transaction requests through the PAaS library.
7. The Payment Application takes over the payment flow and returns the result to your app.
8. Your app prints receipts or stores transaction results as needed.

Library Generations

Library	Artifact	Main class	Integration style
PAaS 2	paaslib_2.0.11.aar	se.westpay.paaslib.service.CarbonTerminal	Kotlin/Android API with Intent transaction launch and typed response parsing.
PAaS 1	posapplib-1.10.0.jar	se.westpay.posapplib.CarbonTerminal	Java API with PaymentTerminal callbacks and direct doTransaction calls.

Use PAaS 2 for new Android integrations unless Westpay has instructed you to integrate with the legacy PAaS 1 library.

Key Capabilities

• Application launch - Allows the Payment Application to discover and start your app.
• Terminal initialisation - Downloads terminal configuration and performs authorisation host login.
• Transaction requests - Starts purchase, refund, and supported terminal transaction flows.
• Transaction results - Converts returned Android Intent data into typed response objects.
• Receipt printing - Prints text or bitmap receipts using the terminal printer.
• Terminal services - Exposes status, printer, navigation bar, sleep/suspend, and other device-level operations.
• Safe exit - Notifies the Payment Application before your app exits.

PAaS 2 Integration Journey

1. Add the se.westpay.paaslib.SIGNATURE intent action to the activity that the Payment Application should launch.
2. Create a shared CarbonTerminal instance in your Android Application class.
3. Call register to connect to the Payment Application service.
4. Call initialise with TerminalSettings.
5. Register an ActivityResultLauncher.
6. Create a PurchaseRequest or RefundRequest.
7. Convert the request to an Intent with createIntentForTransaction.
8. Launch the Payment Application and parse the result with createTransactionResponseFromIntent.
9. Print receipts with startPrintJob.
10. Call notifyExit before closing your app.

Next Steps

• Use Getting Started for the PAaS 2 implementation flow.
• Use PAaS 2 Library for the current AAR API surface.
• Use Transactions for payment request and response handling.
• Use PAaS 1 Library if you maintain a legacy integration.