So, if you are using a Gigaset N720 or the like, and are seeing the error “profile download not possible” when you try to download the settings from the 3CX server, all is not lost.
After toying around with this for some time this evening, I found that the Gigaset units do not currently support TLS 1.2 (which I sure hope they fix soon!). Worse, its not documented that this will be an error issue for you on 3CX forums or Gigaset website.
The fix, for now, is to disable the SSL/SecureSIP Transport and Ciphers in 3CX settings and reboot. Sucky, but works!