Hi, I have read through this forum many comments to a similar problem, but found no solution.
I am running Zoiper on an iPhone with iOS 12.2, using TCP transport, SIP protocol. Against all statements I have found, the phone does not re-register after the registration expiry, when running in the background, i.e. 10 minutes after the registration I get unregistered. According to the SIP server log, the next registration occurs only after I put Zoiper to foreground again.
This happens independently of the setting of "Force background" - which, anyways, is said to be relevant only for UDP transport.
Can the "Use push notifications" solve the problem? Somehow I cannot find any reasonable information what this setting (and buying the subscription, wow) really means...
Btw. using the transport to TLS does not change anything on this behaviour (which I rather expected).