Navigate to FreePBX and enter your credentials.
Select "Connectivity" and click on "Trunks" from the drop-down menu.
Select the pencil icon to edit your Voxtelesys SIP Trunk.
Enter the PJSIP General Settings:
Click on "Submit" when you are finished updating to IP Authentication on your SIP Trunk.
After that, select "Apply Config" to reload FreePBX and finalize your changes.