1. Check whether the Bluetooth headset has sufficient power, if the power is insufficient, please charge it in time
2. Check whether the audio source is mono, you can switch to other music to try.
3. If the audio source is ok, check if the phone is set to mono output
Inspection Method:
IOS system enters the settings --- auxiliary function, check whether the mono audio is turned on or the audio equalizer is biased to the left or right
Android system enters the settings --- barrier-free, check whether the mono audio is turned on or the audio equalizer is biased to the left or right
4. If none of the above is a problem, please refer to: