I couldn’t get several Yealink phones to provision with 3CX V16. Actually, some of the issues started with V15.5. I finally revisited the issue with our recent upgrade to V16 and have finally figured it out.

These are Yealink T46S and T46G phones. The provisioning link was always to port 5000. If you change it from HTTP to HTTPS and the port 5000 to port 5001 then it works!