Follow-up from #2387, which shipped the PaymentMethodMessaging widget as iOS-only.

Why Android was deferred

On Android, Stripe does not expose a PaymentMethodMessagingView. The equivalent is a Compose-based element:

• Class: com.stripe.android.paymentmethodmessaging.element.PaymentMethodMessagingElement
• Artifact: com.stripe:payment-method-messaging (separate from com.stripe:stripe-android)
• Visibility: marked @OptIn(PaymentMethodMessagingElementPreview::class) — preview API
• Usage shape:

  val element = PaymentMethodMessagingElement.create(application)
  // suspend:
  val result: ConfigureResult = element.configure(configuration)
  // compose:
  @Composable fun X() { element.Content(appearance) }

A correct port requires:

1. Adding implementation \"com.stripe:payment-method-messaging:\$stripe_version\" to packages/stripe_android/android/build.gradle.
2. Writing a PlatformView that embeds a ComposeView, runs element.configure(...) off a coroutine scope, reports height via onSizeChanged, and surfaces ConfigureResult.Succeeded / NoContent / Failed back to Dart.
3. Probably bringing in a small StripeAbstractComposeView-style helper, or rolling a Flutter-specific equivalent (ComposeView under an Android PlatformView). This would be the first Compose-based PlatformView in the repo.
4. Possibly extending the Dart model with locale and appearance fields to match the Android Element API surface (Appearance.theme, Appearance.Colors, Appearance.Font).

Reference

• Upstream stripe-react-native wraps this as PaymentMethodMessagingElementView.kt + PaymentMethodMessagingElementConfig.kt. See stripe/stripe-react-native@main:android/src/main/java/com/reactnativestripesdk/.
• stripe-android API surface: stripe/stripe-android@master:payment-method-messaging/api/payment-method-messaging.api.

Current behavior

Until this is implemented, the Dart widget throws UnsupportedError on Android with a pointer back to this issue.

Part of #2378.