To add a SIP client to FreePBX, open the menu “Applications” – “Extensions“, choose for example “Generic CHAN SIP Device” and we indicate the main parameters:
User Extension: 6000 (SIP number)
Display Name: Operator (any name to display)
Secret: PASSWORD
and click “Submit“.
Done, SIP is added, it can already be registered at the specified number and password.
How to add SIP in the configuration file I described in this article – Adding SIP clients to Asterisk