Almost every time I start Zoiper on iOS and try and place a call, the sound only comes out of the iPhone's loudspeaker. There is no sound in the earpiece. The speaker button is not active. Tapping the Speaker button doesn't fix the problem.
One time in 4 or 5, the sound will come out of the earpiece as expected. There seems to be no way to tell whether the sound is going to come from the earpiece or the phone's loudspeaker. Have tried changing phone between silent and ringer mode, have tried force quitting and restarting the Zoiper app.