Apple Watch does not ring but gives a missed call notification

Swipe up for Control Center and check settings like Silent or Theater Mode have not been activated.

Also be cautious if you find the missed call looks like a premium rate or overseas number. It has been a common scam to push out “silent” calls (long enough to register but not long enough to ring) in the hope some suckers will call back and get billed $$$$$$$ per minute to the high cost number.