This is a very common problem.
I wrote a little doc on making agents, but it has some steps, take a look and see if you missed any
https://randomcontributions.blogspot.com/2019/01/issabel-contact-center-installation.html
There are a few key ones.
You must use 4 digit extension numbers
Agent 4 digit numbers MUST be in the DYNAMIC agent box in queue as SXXXX. So if their extension is 4001, it must be S4001 (SIP 4001)
Also, make sure that extension 4001 WORKS. Make sure you can pick it up, dial *43 and hear your voice echo.
ALSO...after you do EVERYTHING right, there is some sort of DELAY between creating the agent and being able to logon. it can be 30 seconds...i've seen it be 2-3 minutes. I suspect their is a database query in the background that needs to happen.
