We use Zoiper 3.8 on an iPhone 6s and 6s Plus with Sipgate as our VoIP provider.
We can call out, but we hear the other side only on the speaker at the bottom of the iPhone and the other side doesn’t hear me. When someone tries to call us it doesn’t ring and they are connected to our mailbox.
This app seams to be useless until I can fix the problems. Please help!