Why does my Wechat voice call fail on my Lumia 640?

[Windows Central Question]

Wechat voice call fails on lumia 640

I have my wechat on my lumia 640 with t-mobile plan. My wechat version is 6.0.6. I could not make/receive voice call from wechat friends, not to speak video call.

The issue has existed since I installed the app 3 months ago. I hope the bug can be fixed during upgrade from wechat. But I still have this issue.

Does this also occur for other lumia phone or lumia 640?

Any one knows the reason and the fix?

Thanks,
Walter