If you cannot auto configure the phone or access the web portal, setup the sip account manually.
- Reset the phone to factory defaults
- Then set the sip line manually.
- The name and authentication name needs to be the ID for the extension in 3cx
- The authentication needs to be the password under ID in 3cx fro the extension
- The other labels should be the user's first and last name.
- Reboot the phone.