We just did a rollout of Zoiper to a dozen people. Those using Android are able to register without issues, irrespective of whether they're on a 3G, LTE or WiFi network. They're also able to receive calls just fine.
However, those with iPhones are all struggling. If we don't use the PUSH server, then registration works, but the registration is lost after about a minute so inbound calls won't work.
When enabling the PUSH server, we get a few different errors, but the most prevalent of which are "Push server is unable to connect to home register server" and "Bad request - missing push device token". These errors occur on both WiFi and 3G/LTE networks.
What are we missing with the iPhone setup to get it to work?