[firebase_messaging]: iOS plugin labels the APNs token as Prod on every non-DEBUG build, so development-signed release builds register a sandbox token as production and FCM sends fail (invalid-argument) on about half the launches

Read ios/firebase_messaging/Sources/firebase_messaging/FLTFirebaseMessagingPlugin.m, focusing on application:didRegisterForRemoteNotificationsWithDeviceToken: and ensureAPNSTokenSetting. Check how both call sites set the APNs token type and compare with the Firebase iOS SDK behavior described in the issue. Done when development-signed release builds register sandbox tokens correctly and the reported FCM send failure is resolved, while store and debug builds retain the expected behavior.

Is there an existing issue for this?

• I have searched the existing issues.

Which plugins are affected?

Messaging

Which platforms are affected?

iOS

Description

On iOS the plugin decides the APNs token type at compile time:

// ios/firebase_messaging/Sources/firebase_messaging/FLTFirebaseMessagingPlugin.m (17.0.1)
// application:didRegisterForRemoteNotificationsWithDeviceToken: and ensureAPNSTokenSetting
#ifdef DEBUG
  [messaging setAPNSToken:deviceToken type:FIRMessagingAPNSTokenTypeSandbox];
#else
  [messaging setAPNSToken:deviceToken type:FIRMessagingAPNSTokenTypeProd];
#endif

DEBUG is only a proxy for the APNs environment. A release build installed with a development provisioning profile (what flutter run --release on a physical device does with automatic signing) has aps-environment = development and therefore a sandbox APNs token, but the plugin registers it as Prod. The same holds for a profile build. The Firebase iOS SDK already knows the right answer: FIRMessagingAPNSTokenTypeUnknown makes FIRMessagingIsSandboxApp() read aps-environment from embedded.mobileprovision (and defaults to production when the profile is stripped, i.e. App Store / TestFlight), which is exactly what the SDK's own FIRMessagingRemoteNotificationsProxy passes ([FIRMessaging messaging].APNSToken = deviceToken).

Because both hooks run as GoogleUtilities app-delegate interceptors on the same callback, and setAPNSToken:type: returns early when the token data is unchanged, whichever interceptor runs first decides the environment for that launch. GULAppDelegateSwizzler notifies interceptors from an NSDictionary keyed by object address, so the order is not stable. With FirebaseMessagingInstallationIdEnabled = YES the registration (FIRMessagingFIDRegisterOperation) sends apns_environment: PROD for a sandbox token on the launches where the plugin wins, and every send to that Installation ID then fails:

FCM HTTP v1 messages:send -> 400 INVALID_ARGUMENT "APNs device token is invalid."
Admin SDK sendEachForMulticast -> messaging/invalid-argument

On the launches where the SDK's proxy wins, the same install works. Across 11 apps on one iPhone we saw both outcomes on the same app and build, in streaks (one app lost 4 launches in a row, then won; another: 2 wins, 7 losses, 2 wins ...). A debug build of the same app (plugin says Sandbox) delivers every time.

Store builds are not affected (both paths say production). The impact is on development-signed release/profile builds, i.e. every flutter run --release smoke test and every internal app that is sideloaded rather than published, and it is silent on the device: the registration succeeds, only the server sees the 400.

Expected: the plugin passes FIRMessagingAPNSTokenTypeUnknown (let the SDK derive the environment from the provisioning profile, as the SDK does itself) or otherwise derives the type from aps-environment rather than from DEBUG. One-line change in both call sites; behaviour for App Store / TestFlight / Ad Hoc / Debug builds is unchanged, since the SDK's detection gives the same answer there.

Workaround we use: FirebaseMessagingAutoInitEnabled = NO in Info.plist (the plugin's interceptor is a no-op while auto-init is off, and register() is called from Dart as documented under "Prevent auto initialization"), plus a native call to registerForRemoteNotifications() once the default FirebaseApp exists, so the SDK's proxy is the only one that labels the token. It works deterministically, but it should not be necessary.

Reproducing the issue

1. New Flutter app, firebase_core 5.1.0, firebase_messaging 17.0.1, flutterfire configure; Info.plist: FirebaseMessagingInstallationIdEnabled = YES (default auto-init). Push Notifications capability on; APNs key uploaded in the Firebase console (key enabled for Sandbox & Production).
2. In Dart, after Firebase.initializeApp() and requestPermission(): subscribe to FirebaseMessaging.instance.onRegistered, call register(), print the Installation ID.
3. flutter run --release -d <physical iPhone> with automatic signing (Xcode uses the development profile; codesign -d --entitlements - build/ios/iphoneos/Runner.app shows aps-environment = development).
4. Send to the printed id with the FCM HTTP v1 API: POST https://fcm.googleapis.com/v1/projects/<project>/messages:send body {"message":{"fid":"<id>","notification":{"title":"t","body":"b"}}}.
5. Result on roughly half of cold launches: HTTP 400 "APNs device token is invalid."; on the other launches: 200 and the push arrives. Kill and relaunch the app and send again to see it flip. The debug build (flutter run) of the same app answers 200 every time.

To make it deterministic, break on -[FIRMessaging setAPNSToken:type:]: the first call on a failing launch comes from FLTFirebaseMessagingPlugin with type 2 (Prod); on a working launch from FIRMessagingRemoteNotificationsProxy with type 0 (Unknown).

Firebase Core version

5.1.0

Flutter Version

3.47.9 (stable), Dart 3.13.7

Relevant Log Output

# FCM HTTP v1, fid registered by a development-signed release build on a launch where the plugin's hook ran first
HTTP 400
{"error":{"code":400,"message":"APNs device token is invalid.","status":"INVALID_ARGUMENT"}}

# Admin SDK (firebase-admin 14.5.0) sendEachForMulticast({ fids: [...] }) on the same registration
messaging/invalid-argument

# entitlements of the installed build
codesign -d --entitlements - Runner.app | grep -A1 aps-environment
<key>aps-environment</key>
<string>development</string>

Flutter dependencies

firebase_core: 5.1.0
firebase_core_platform_interface: 8.1.1
firebase_messaging: 17.0.1
firebase_messaging_platform_interface: 4.11.1
Firebase iOS SDK (SPM): 13.1.1
GoogleUtilities (SPM): 8.1.5
Xcode 27.2, macOS 27.2, physical iPhone 15 Pro Max

Additional context and comments

• The #ifdef DEBUG split dates from the 2020 roadmap rework (#4012) and the same two sites were touched in July 2026 (6f22596) without changing the rule.
• The documented alternative ("Prevent auto initialization", FirebaseMessagingAutoInitEnabled = NO + register()) does avoid the mislabel, but with auto-init off the plugin no longer calls registerForRemoteNotifications at all, so an app must do that natively; that combination is probably not what most users expect from the docs.
• Happy to open a PR if the FIRMessagingAPNSTokenTypeUnknown approach is acceptable.