FreePBX 17 Contacts don't show on P325

My outside IT help has just installed 18 Sangoma P325 phones to with FreePBX 17. We cannot get the contacts to populate on the phones themselves. The phone button just takes us to an empty screen. What are the basic places to make sure things are set properly to share the internal contacts to each phone?

Endpoint Manager - Global Settings - here use hostnames (not IP addresses) and make sure you have HTTPS working with a valid certificate. The P phones get their contacts by HTTPS REST calls to the PBX and this won’t work by IP.

We will get a certificate setup and test. I will let you know if that works.

Another basic thing that might not be a thing but that has tripped us up in the past is that each extension needs a user assigned to it for the phones to be able to access the phone apps.