Hi, I have smartphone Asus with Android 5. I use IAX2. I installed Zoiper and ZoiperBeta and try to call.
I get an error "Network is busy" and anyusers can't call me too.
When I use these credentials by laptop or android 4 - it is OK
This error is returned from the server in case the caller is busy (on the phone) or for some reason the whole network is busy. Check with your provider for more details.