If push notifications are not supported by your SIP server, then the app can use our SIP-PUSH proxy service by default.
We provide this service for free for all our customers and we don't store any credentials, even the service logs are auto-deleted after 3 days.
You can turn it off from the app settings (disable push notification) if you wish.

Push notification is useful so that you can receive incoming calls even if the app is not running or your device is sleeping. Otherwise it is also possible to run the app as a background service to handle incoming calls. This will use some more battery. You can also disable both service and push if you are not interested in incoming calls.

This should be fixed with the latest upgrade.
If somehow the problem still peristis, please send a log so we can look for the details.

See this wiki post about the details:
https://www.mizu-voip.com/Support/Wik...ic=Android+logs

So, you just need to enable the logs, reporduce the problem and upload the logs. Don't restrat the app between the problem happened and the log upload.
The log will/should contain the app startup (with the relevant parameters) and the failed register/call.