Flutter SDK (faststar_pay)

The official Flutter SDK opens the FastStar hosted checkout in a full-screen WebView inside your app and returns the payment result through callbacks — no WebView plumbing required.

Installation

dependencies:
  faststar_pay: ^1.0.0

The package depends on webview_flutter ^4.0.0:

  • Android: minSdkVersion 19 (21+ recommended)
  • iOS: iOS 12.0+, no extra configuration

Opening the checkout

import 'package:faststar_pay/faststar_pay.dart';

await FastStarCheckout.open(
  context,
  url: checkoutUrl, // Checkout Session url created by your server, or a payment link
  onSuccess: (data) {
    // Payment succeeded (fulfill orders from the server-side webhook)
    debugPrint('paid payment_intent_id=${data['payment_intent_id']}');
  },
  onCancel: () {
    debugPrint('buyer canceled');
  },
  onError: (data) {
    debugPrint('payment failed: ${data['message']}');
  },
);

open() pushes a full-screen checkout page that includes:

  • an AppBar close button (triggers onCancel)
  • a page-load progress bar
  • system back gesture mapped to onCancel

Return value instead of callbacks

open() also returns a Future<FastStarCheckoutResult> you can simply await: 

final result = await FastStarCheckout.open(context, url: payUrl);

switch (result.event) {
  case FastStarCheckoutEvent.success:
    print('success: ${result.data}');
  case FastStarCheckoutEvent.cancel:
    print('canceled');
  case FastStarCheckoutEvent.error:
    print('failed: ${result.data}');
}

How results come back: FastStarBridge + URL fallback

The SDK receives the checkout result over two channels. Either one completes the flow, and your callback is guaranteed to fire only once:

  1. JS bridge (primary): the SDK injects a JavaScript channel named FastStarBridge. The hosted checkout page calls 
    window.FastStarBridge.postMessage(JSON.stringify({
  event: 'checkout.success', // checkout.success | checkout.cancel | checkout.error
  data: { payment_intent_id: 'pi_xxx' }
}));
    The channel accepts strings only, so the payload is JSON-stringified; unlike the iframe message format, no source field is needed because the channel itself is isolated. The shorthand event names success / cancel / error are also accepted.
  2. URL interception (fallback): when the checkout page redirects to your success_url / cancel_url with a faststar_status=success|cancel|error query parameter, the SDK blocks the navigation, closes the checkout page and fires the matching callback. Any other query parameters on the URL (such as payment_intent_id) are passed through to your callback as data. So even if a checkout page never calls the bridge, a normal redirect still completes the flow.

Notes

  • onSuccess is for client-side interaction only (closing the page, showing a success screen). Order fulfillment must rely on FastStar's server-side webhooks.
  • 3-D Secure bank verification happens inside the same WebView; no extra handling is needed.