Hello @zoiper_user,
Is it working when the application is open? (I ask, because you might just have problem with non persistent connections, hence the calls cannot come in. Push notification is what you need in that case.)
- Make sure in your voip.ms account that you have a good connection.
- Use TLS secured connection over TCP (as a roaming phone will never be able to get calls properly. The phone needs to keep the connection to the server, and this is the most easy way. So use TLS. Look at the wiki for that.
https://wiki.voip.ms/article/Call_Encryption_-_TLS/SRTP
(Look at the wiki for your good Zoiper version and see specific instructions for it.)
Even with that, you might miss calls because the phone goes into battery saving mode, etc. So Push Notification is required. With Zoiper you have to pay every month for that.
You may instead try the free voip.ms softphone application.
You can also buy Groundwire (quite cheap, same application, full featured). See my experience here:
Kind regards!