Problems registering with zoiper

Problems registering with zoiper (Android)

PROBLEM:
Zoiper stays on Registering for long time
After some time it displays: registration failed (dns timeout 503)

This happens whether on wifi / 4G


WORKAROUND:
The workaround was to enter on settings > connectivity and then go back (exit), which would cause Zoiper to restart completely.


But I was tired of doing that and researching and testing found the following solution:


SOLUTION:
Settings > Connectivity > Listening Ports > Disable all the boxes so no port is random.

After doing that it stays registered even after changing networks or stopping zoiper.