Xcode's Background Assets Run scheme option

I just saw the following in the Xcode 27 release notes:

Xcode can now serve asset packs to your app while debugging on devices by setting a Background Asset Packs folder in the Run scheme action’s Options tab. (165230494)

And sure enough, the option is there.

But what do I need to point this to? I tried everything:

• the path to the built .aar asset pack
• the path to the .json manifest file
• the path to the download-manifest.json (for self-hosted asset packs)
• the path to the directory that actually contains the assets (as also referenced by the manifest file)
• the path to the directory that contains the manifest file and the asset directory.

Nothing works. I always get the same errors on the console:

Checking for updates failed: DecodingError.dataCorrupted: Data was corrupted. Debug description: The given data was not valid JSON.. Underlying error: Error Domain=NSCocoaErrorDomain Code=3840 "Unexpected end of file" UserInfo={NSDebugDescription=Unexpected end of file}
The asset pack with the ID “MyID” couldn’t be looked up: DecodingError.dataCorrupted: Data was corrupted. Debug description: The given data was not valid JSON.. Underlying error: Error Domain=NSCocoaErrorDomain Code=3840 "Unexpected end of file" UserInfo={NSDebugDescription=Unexpected end of file}
The manifest couldn’t be refreshed: DecodingError.dataCorrupted: Data was corrupted. Debug description: The given data was not valid JSON.. Underlying error: Error Domain=NSCocoaErrorDomain Code=3840 "Unexpected end of file" UserInfo={NSDebugDescription=Unexpected end of file}

I'm testing on a physical iPhone.

Any advice would be appreciated!