Phone Auth: checkNotificationForwarding() probe fails on first try (real device, no session cache issue) — verifyPhoneNumber throws notificationNotForwardedError

[tb6gw7wvf6-dev]

Description

Description

PhoneAuthProvider.verifyPhoneNumber fails immediately with notificationNotForwardedError
on a real device (TestFlight release build), on the very first attempt after a cold app launch
(not a session-cache artifact — tested explicitly).

Root cause identified (source read)

AuthNotificationManager.checkNotificationForwarding() sends a local fake probe notification
via application.delegate.application(_:didReceiveRemoteNotification:fetchCompletionHandler:)
and waits kProbingTimeout = 1.0 second for it to be routed back through
AuthNotificationManager.canHandle(notification:). If this 1s local round-trip fails, the SDK
throws directly — PhoneAuthProvider.internalVerify never reaches the reCAPTCHA fallback
(AuthRecaptchaVerifier switch is unreachable).

What we've verified as correct (ruling out app misconfiguration)

• APNs Auth Key correctly uploaded (Cloud Messaging), correct Key ID/Team ID
• Push Notifications capability enabled on App ID
• aps-environment = production in release entitlements
• Phone provider enabled, SMS region policy allows the test region
• API key: Identity Toolkit + Token Service APIs allowed, no blocking application restriction
• REVERSED_CLIENT_ID correctly registered as URL scheme
• FirebaseAppDelegateProxyEnabled absent (swizzling enabled by default)
• Single UIApplicationDelegate, no conflicting delegate, no SceneDelegate interference
  (confirmed GULSceneDelegateSwizzler only swizzles scene:openURLContexts:, never
  notification methods)
• didReceiveRemoteNotification has the exact expected signature (with
  fetchCompletionHandler), matches the selector Firebase looks for byte-for-byte
• APNs device token IS received (FirebaseMessaging.instance.getAPNSToken() returns non-null
  at call time — confirmed via on-device logging)
• App Check (App Attest) registered, monitoring mode (not enforced)
• appVerificationDisabledForTesting never set (would be test-only anyway)
• Tested explicitly on FIRST attempt after full app kill+relaunch — not a repeated-session
  cache issue (session cache at AuthNotificationManager.swift:45,91 was considered and ruled
  out this way)

Suspicion

The 1-second timeout for a purely local delegate round-trip (no network involved) may be too
short on some real devices/launch conditions, and there's no retry once cached as failed for
the session — but here it fails even on the very first attempt, suggesting either the timeout
is sometimes insufficient on cold launch, or another condition prevents
canHandle(notification:) from being reached in time.

Environment

• firebase_auth: 5.7.0 (FlutterFire)
• Firebase iOS SDK: vendored via CocoaPods (version bundled with firebase_auth 5.7.0)
• Device: iPhone 13, iOS 26.6.2, real device via TestFlight (release build)
• Flutter stable

Steps to reproduce

1. Real device, release/TestFlight build
2. Fresh app launch (kill previous instance first)
3. Navigate directly to phone sign-in, enter valid number, tap send — first and only action
4. verifyPhoneNumber completion handler receives notificationNotForwardedError immediately

Expected

Either the probe succeeds, or a graceful fallback to reCAPTCHA occurs.

Reproducing the issue

No response

Firebase SDK Version

5.7.0

Xcode Version

15.4

Installation Method

CocoaPods

Firebase Product(s)

Authentication

Targeted Platforms

iOS

Relevant Log Output

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If using CocoaPods, the project's Podfile.lock

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