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error Bose
Error Code Fast blinking red
Error state indicated by fast blinking red light on the Power/Bluetooth indicator or headphone charging indicator.
✓ How to Fix It
Remove the headphones from the charging case and allow them to return to normal operation. If the error persists, try resetting the connection by placing earbuds in the case and removing them again.
Source: page 22 of the official manual
From the manual
This error code appears in:
Bose QuietComfort Ultra Earbuds