Checkout for apps

// Your server, with your API key (never in the app).
const res = await fetch("https://api.vezmo.com/api/v1/merchant/secure-payments", {
  method: "POST",
  headers: {
    Authorization: `Bearer ${accessToken}`,
    "Content-Type": "application/json",
    "Idempotency-Key": order.id,
  },
  body: JSON.stringify({
    title: `Order #${order.number}`,
    amount: order.total, // 49.00
    currency: "USD",
    client: { name: buyer.name, email: buyer.email, country: "US", postalCode: "10001" },
    // Registered under Developers → Mobile apps (a path or query under it is fine too).
    app: { returnUrl: "acme://vezmo" },
  }),
});
const { data } = await res.json();

// Send these two to your app:
// data.securePayment.url          the checkout page
// data.securePayment.clientToken  for GET …/status

import * as WebBrowser from "expo-web-browser";

export async function payOrder(checkoutUrl: string) {
  // The phone's secure browser sheet, closed for you when the checkout opens acme://vezmo.
  const result = await WebBrowser.openAuthSessionAsync(checkoutUrl, "acme://vezmo");

  if (result.type === "success") {
    const url = new URL(result.url);
    const status = url.searchParams.get("status"); // "success" | "pending" | "failed"
    const paymentId = url.searchParams.get("paymentId");
    return { status, paymentId };
  }
  // The buyer closed the sheet without finishing: ask the session status.
  return { status: "closed" };
}

import AuthenticationServices
import UIKit

final class WebCheckout: NSObject, ASWebAuthenticationPresentationContextProviding {
  private var session: ASWebAuthenticationSession?

  func open(_ checkoutURL: URL, completion: @escaping (_ status: String?, _ paymentId: String?) -> Void) {
    // The checkout ends on acme://vezmo?status=…&paymentId=…, which closes the sheet.
    let session = ASWebAuthenticationSession(url: checkoutURL, callbackURLScheme: "acme") { url, _ in
      let items = url.flatMap { URLComponents(url: $0, resolvingAgainstBaseURL: false)?.queryItems }
      completion(
        items?.first { $0.name == "status" }?.value,     // "success" | "pending" | "failed"; nil = closed
        items?.first { $0.name == "paymentId" }?.value
      )
    }
    session.presentationContextProvider = self
    // Keep the browser's cookies: some bank and pay-later pages need them.
    session.prefersEphemeralWebBrowserSession = false
    self.session = session
    session.start()
  }

  func presentationAnchor(for session: ASWebAuthenticationSession) -> ASPresentationAnchor {
    UIApplication.shared.connectedScenes
      .compactMap { ($0 as? UIWindowScene)?.keyWindow }
      .first ?? ASPresentationAnchor()
  }
}

// build.gradle.kts: implementation("androidx.browser:browser:1.8.0")
import android.net.Uri
import androidx.browser.customtabs.CustomTabsIntent

fun openCheckout(context: android.content.Context, checkoutUrl: String) {
  CustomTabsIntent.Builder().build().launchUrl(context, Uri.parse(checkoutUrl))
}

<!-- AndroidManifest.xml: the activity that receives acme://vezmo -->
<activity
    android:name=".CheckoutReturnActivity"
    android:exported="true"
    android:launchMode="singleTop">
  <intent-filter>
    <action android:name="android.intent.action.VIEW" />
    <category android:name="android.intent.category.DEFAULT" />
    <category android:name="android.intent.category.BROWSABLE" />
    <data android:scheme="acme" android:host="vezmo" />
  </intent-filter>
</activity>

class CheckoutReturnActivity : AppCompatActivity() {
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    handle(intent)
  }

  override fun onNewIntent(intent: Intent) {
    super.onNewIntent(intent)
    handle(intent)
  }

  private fun handle(intent: Intent) {
    val link = intent.data ?: return
    val status = link.getQueryParameter("status")       // "success" | "pending" | "failed"
    val paymentId = link.getQueryParameter("paymentId")
    // Show the result, then refresh the order from your server (fulfilled by the webhook).
  }
}

// pubspec.yaml: flutter_web_auth_2
import 'package:flutter_web_auth_2/flutter_web_auth_2.dart';

Future<Map<String, String?>> payOrder(String checkoutUrl) async {
  try {
    final result = await FlutterWebAuth2.authenticate(
      url: checkoutUrl,
      callbackUrlScheme: 'acme', // the sheet closes when the checkout opens acme://vezmo
    );
    final link = Uri.parse(result);
    return {
      'status': link.queryParameters['status'], // success | pending | failed
      'paymentId': link.queryParameters['paymentId'],
    };
  } catch (_) {
    // The buyer closed the sheet without finishing: ask the session status.
    return {'status': 'closed'};
  }
}