I might need to get help from some other FreePBX people to figure this one out… let me think about it for a bit.
The reason I thought there was a problem with your _custom file is because the endpoint itself is declared in that file with this block:
and so in the trunk creation in the FreePBX GUI you set the Custom Dial String (which points to that block/endpoint)
Custom Dial String: PJSIP/$OUTNUM$@gvsip1
So to me it seems you setup the trunk, and its looking for gvsip1 but its not seeing it anywhere, so to me it seems like your _custom file is not loading or is broken.
Hopefully somebody else comes along that can help, and if I think of anything I will let you know…