I have a 3CX hosted PBX with an on-prem SBC. I have setup 3CX according to the following link. https://www.3cx.com/voip-gateways/grandstream-ht-fxs/. I have also uploaded the xml configuration file to the HT814 and setup the FXS authentication for the fax. The HT814 shows as a new phone with the loopback address. I cannot make or receive calls through the HT814 although the HT814 web interface shows the extension registered. What am I missing?
What you see here is the PnP message, you can safely ignore that. Select the device and click the reject button on top if you want that to go away.
It looks like you setup a FAX extension 8800 and it appears to be registered correctly, so that won't show up in the phones page when registered. It will show up here since we consider it a system extension: