KZ Z1 charging problems

Noobie and always looking for value for money.

I bought KZ Z1 IEMs because of good reviews. Been using it and love what I hear. But I notice that it never charges. I put it in the charging box when it’s plugged and unplugged. Doesn’t make a difference. Has anyone had this problems with KZ Z1 or any chargeable IEMs for that matter? How did you solve it? Thanks!