Connect Plantronics IP40 on a FreePBX

Hello, I’m new onto the freepbx

I have some Plantronics IP-40 stations i would like to connect onto my freepbx so it can function as sip server for our telephony platform.

It’s only internal communication so no external connections are needed.
Has anyone got any experience with this or can help me out?

I tried to add an extension and tried to connect my ip-40 onto my freepbx server but the status is still registering…

kind regards