- Edited
@MattD Would it be possible to reach out to them and ask them if they use SafetyNet/Play Integrity API? If they do, this would be why the app refuses to run on GrapheneOS...
At that point, they'd either have to stop doing that, or specifically whitelist GrapheneOS, for which the team provides a guide for developers to do so:
https://grapheneos.org/articles/attestation-compatibility-guide