Spotify iOS SDK 5.0.1 App Remote Authentication Returns error=unknown_error with No Access Token

[ABenAfia]

Plan
Premium

Operating System
iOS 26.4.2

My Question or Issue

We are experiencing a persistent authentication issue with Spotify App Remote integration using the Spotify iOS SDK.

Environment:

• Spotify iOS SDK version: 5.0.1 (integrated manually as an XCFramework)
• Authentication method: SPTAppRemote
• Spotify application version: 9.1.48.1659
• Spotify account type: Premium

Observed behavior:

1. Our application successfully launches the Spotify app.
2. The user authenticates on the Spotify side.
3. Spotify successfully redirects back to our application.
4. Instead of returning an access token, Spotify redirects with the following parameters:

error=unknown_error
error_description=An unknown error has occured
spotify_version=9.1.48.1659

As a result, no access token is issued and App Remote cannot establish a connection.

Investigation performed:

• Redirect URI configuration verified.
• URL scheme callback verified and working correctly.
• Client ID and application configuration verified.
• Premium account used for testing.
• App switching between our application and Spotify works correctly.
• The issue reproduces on both development and App Store production builds.
• We tested using App Remote only and removed mixed SessionManager/AppRemote implementations.

Most importantly, we reproduced the exact same issue using Spotify's official iOS SDK demo application. The demo application also receives:

error=unknown_error
error_description=An unknown error has occured
spotify_version=9.1.48.1659

and no access token is returned.

Since the callback reaches our application correctly and the issue is reproducible using Spotify's official sample application, we suspect the failure may originate from the Spotify application, backend authentication service, or an App Remote compatibility issue rather than our application code.

Could you please advise:

• Are there any known issues affecting App Remote authentication or token issuance?
• Is Spotify aware of any compatibility issues between Spotify App 9.1.48.x and Spotify iOS SDK 5.0.1?
• Are there any recent platform or policy changes that could cause error=unknown_error responses?
• Is there any additional diagnostic information that we can provide to help identify the root cause?

We can provide additional logs, screenshots, screen recordings, and reproduction steps if necessary.