As I just said in the second post you must have created about this. You’re doing this wrong. You just can’t add stuff to sip.conf, that’s not where FreePBX writes out peer details. Also you just can’t add something to the .conf file and expect the GUI just to see it. Again, extension details are held in the SQL database and the AstDB so if nothing was added there, Asterisk is going to see the SIP peer and let you auth because it’s a peer but there is nothing in the dialplan, AstDB or anything for the PBX to realize calls should be sent to this peer, etc. It won’t have the proper settings for inbound/outbound calling.
There are methods to add this stuff via the system CLI or APIs but doesn’t seem like you’re using them.