QCY T1 User Manual page 29

FAQ
Compatibility with Bluetooth 4.0
The headphones are backwards compatible. This means that you can use the headphones
with older devices.
Note, however, that the range and sound quality of the headphones may be reduced.
We strongly recommend a device that supports Bluetooth 5.0.
A headphone is louder than the other?
First reset the headphones to factory settings.
If the problem persists, please check the music volume sync of your smartphone.
Anroid: Settings> Connections> Bluetooth> top right of the 3 small dots.
Iphone: Settings> Music> Auto Adjust Volume> Disable.