Sound on voice call via Earfun Air Pro 4 call sound volume is very low, even at 100% volume?

Trying to get volume higher, realized OP12 and earfun buds are not in sync.. When I tapped buds, saw only 50% volume.. Not good. 

Hi Friend,

Thanks for choosing EarFun. Sorry for the inconvenience caused to you.

Please kindly send your order number to our customer service team: service@myearfun.com or submit the warranty ticket on our official website: https://www.myearfun.com/process-warranty.

Sincerely,

EarFun

I'm having the same problem.

I created my own thread.