Diagnosis
The capacitive touch panel is disabled, locked, or has a software glitch. It is not a hardware failure.
How to Fix It
Check if Touch Controls are locked. Press and hold the volume down (-) button on top for 3 seconds. You should hear a tone. This toggles the lock. Try tapping play/pause. If it works, they were locked.
If That Didn't Work
Perform a power cycle. Unplug the power cord from the back of the speaker. Wait 60 seconds. Plug it back in. Allow the speaker to fully boot. The touch controls should reinitialize.
Heads Up
Touch controls can be disabled in the Sonos app under Settings > System > Your Era 100 > Touch Controls. Verify they are set to "Enabled" and not "Volume Only" or "Disabled."