DIAGNOSIS
One of the two 1.6" front-firing speakers has likely failed or become disconnected, or a software setting has changed.
FIX
Check the audio balance. Swipe down from the top > Settings > Sound. Adjust the Bass, Midrange, and Treble sliders. Test by playing music. If sound returns, reset the sliders to the middle position. Perform a device reboot by holding the Action button for 25 seconds.
IF THAT DIDN'T WORK
This indicates a probable hardware failure with a speaker driver or internal connection. Contact Amazon Support for diagnostics. The audio system is not user-serviceable.
HEADS UP
Before contacting support, test with multiple audio sources (e.g., Amazon Music, a news briefing, a video call) to confirm the issue is consistent. Rule out a problem with a single streaming service.