Hi.. every box tends to have its own compatibility issues with certain apps. But the GT-King shouldn’t with HBO Max. No audio is probably a codec or connection issue. How’s your audio connected?

Hmm, that’s a simple connection and it should work. Try the following in succession and hopefully one works.
*Ensure you have the latest app version. If not, update.
*Clear app data & cache. Then log back in again.
*Uninstall current latest version. Install previous app version. Cuz sometimes the latest version update of an app might have more bugs, making it problematic.
*Factory reset to try again on clean slate.... if this still doesn’t work? You probably just have to wait for the next app update, where hopefully that issue is fixed.