I have an AR750S-EXT and I am experiencing the same error message “WARNING: No cable is plugged into the WAN port!” when I try to switch to AP mode. I found this page when searching for the error.

I have a device connected on the WAN port, the error message is not correct. Also, I tried using the option “WAN port has been used as LAN. You can set it back to WAN below.” in the Internet page as well. This did not help either.

The only reason I bought this device is because I want AP mode, where it simply passes packets from one of the ports on to the WiFi, so I really need this feature to work. I’m running the latest firmware 3.025 compiled on 2019-06-26 11:15:03.

Thanks!