the problem you have is Android 5.1 is out of support. as well was 6 and 7. Only 8+ are currently supported and not EOL. This means that many software versions will not work on the older unsupported versions.
Welcome to our Community Help Forums 🙂 thank you for your first post regarding our TV Connect App. Unfortunately, the Android 5.1 is now out of support meaning that the Connect App will no longer work on your phone. Apologies for the inconvenience 😞