Claps are missed
Move the phone out of a thick bag or closed drawer, use two clear claps, then raise sensitivity one step.
Help
Start with a quick sound test and alert test
Music or speech triggers it
Lower the matching sensitivity, require two or three claps, and use a longer cooldown.
A whistle is missed
Use one steady note rather than a tune. Test from the place where you normally leave the phone.
Another app needs the microphone
Calls, camera apps, recorders, and assistants can interrupt listening. The app retries and shows an honest error if it cannot recover.
The alert is silent
Enable Ring, check alarm volume, and run Test alert with your usual Do Not Disturb and Bluetooth setup.
The light does not flash
Enable Flashing light and allow camera access. Ring and vibration still work when a flash is unavailable.