PaymentSheet IntentMode doesn't support SetupIntents

[ztaylor54]

The Stripe docs describe how to collect payment details before creating an Intent, but the flutter platform interface doesn't properly implement the IntentMode enum:

flutter_stripe/packages/stripe_platform_interface/lib/src/models/payment_sheet.dart

Lines 139 to 155 in 749a4d2

	@freezed
	class IntentMode with _$IntentMode {
	@JsonSerializable(explicitToJson: true)
	const factory IntentMode({
	required String currencyCode,
	required int amount,
	/// Data related to the future payment intent
	IntentFutureUsage? setupFutureUsage,
	/// Capture method for the future payment intent
	CaptureMethod? captureMethod,
	}) = _IntentMode;
	factory IntentMode.fromJson(Map<String, dynamic> json) =>
	_$IntentModeFromJson(json);
	}

Note how the IntentMode class requires currencyCode and amount, but the platform implementations expect amount and currencyCode to be nullable when reading them, and use that information to determine whether to configure the payment sheet for a PaymentIntent or SetupIntent:

flutter_stripe/packages/stripe_ios/ios/Classes/Stripe Sdk/StripeSdk+PaymentSheet.swift

Lines 217 to 253 in 749a4d2

	private func buildIntentConfiguration(
	modeParams: NSDictionary,
	paymentMethodTypes: [String]?,
	captureMethod: PaymentSheet.IntentConfiguration.CaptureMethod
	) -> PaymentSheet.IntentConfiguration {
	var mode: PaymentSheet.IntentConfiguration.Mode
	if let amount = modeParams["amount"] as? Int {
	mode = PaymentSheet.IntentConfiguration.Mode.payment(
	amount: amount,
	currency: modeParams["currencyCode"] as? String ?? "",
	setupFutureUsage: modeParams["setupFutureUsage"] != nil
	? (modeParams["setupFutureUsage"] as? String == "OffSession" ? .offSession : .onSession)
	: nil,
	captureMethod: captureMethod
	)
	} else {
	mode = PaymentSheet.IntentConfiguration.Mode.setup(
	currency: modeParams["currencyCode"] as? String,
	setupFutureUsage: modeParams["setupFutureUsage"] as? String == "OffSession" ? .offSession : .onSession
	)
	}
	return PaymentSheet.IntentConfiguration.init(
	mode: mode,
	paymentMethodTypes: paymentMethodTypes,
	confirmHandler: { paymentMethod, shouldSavePaymentMethod, intentCreationCallback in
	if (self.hasEventListeners) {
	self.paymentSheetIntentCreationCallback = intentCreationCallback
	self.sendEvent(withName: "onConfirmHandlerCallback", body: [
	"paymentMethod": Mappers.mapFromPaymentMethod(paymentMethod) ?? NSNull(),
	"shouldSavePaymentMethod": shouldSavePaymentMethod
	])
	} else {
	RCTMakeAndLogError("Tried to call confirmHandler, but no callback was found. Please file an issue: https://github.com/stripe/stripe-react-native/issues", nil, nil)
	}
	})
	}

flutter_stripe/packages/stripe_android/android/src/main/kotlin/com/reactnativestripesdk/PaymentSheetFragment.kt

Lines 409 to 428 in 749a4d2

	private fun buildIntentConfigurationMode(modeParams: Bundle): PaymentSheet.IntentConfiguration.Mode {
	val currencyCode = modeParams.getString("currencyCode")
	?: throw PaymentSheetException("You must provide a value to intentConfiguration.mode.currencyCode")
	return if (modeParams.containsKey("amount")) {
	PaymentSheet.IntentConfiguration.Mode.Payment(
	amount = modeParams.getInt("amount").toLong(),
	currency = currencyCode,
	setupFutureUse = mapToSetupFutureUse(modeParams.getString("setupFutureUsage")),
	captureMethod = mapToCaptureMethod(modeParams.getString("captureMethod")),
	)
	} else {
	val setupFutureUsage = mapToSetupFutureUse(modeParams.getString("setupFutureUsage"))
	?: throw PaymentSheetException("You must provide a value to intentConfiguration.mode.setupFutureUsage")
	PaymentSheet.IntentConfiguration.Mode.Setup(
	currency = currencyCode,
	setupFutureUse = setupFutureUsage
	)
	}
	}

Both iOS and Android configure the payment sheet for a SetupIntent when amount is null. It is interesting (and perhaps a separate bug?) to note that while iOS allows currencyCode to be null on a PaymentIntent, Android does not.

Resolution

I think the easiest fix here would be to make IntentMode.amount a nullable field. Freezed does support union types, but that would get messy and would require updates to the individual platform implementations.

Hopefully this can get resolved quicky, because as of now there is no way to use a SetupIntent for a deferred payment in the manner described in the Stripe documentation. If you attempt to just specify a bogus amount, the payment sheet returns an error because it tries to fetch a PaymentIntent that doesn't exist: