Zoiper on my OnePlus 3T running 7.1.1 hasn't worked for awhile. I finally figured out that it is the Voice over Wifi setting that is causing the problem. If I disable VoWifi and reboot, Zoiper works normally. With it on, I cannot register with either my PBX on my LAN or my VOIP service directly.
Does anyone know how to get both working at the same time? I would like to be able to use VoWifi for my cell service but still use Zoiper.