Thank for your time, this closed
That saying there has been an attempt to call a non-existent Asterisk dialplan function, which is a coding error. Google cannot find this name anywhere but in your posting, and I certainly don’t recognize it as part of Asterisk. It is just possible that a commercial modules is using a FreePBX modification to Asterisk, but it sounds more likely that “()” has been, wrongly, added after a variable name.
It has nothing to do with SIP registration.