[E] at :0 - "serialnmea: No known GPS device found. Specify the COM port via QT_NMEA_SERIAL_PORT."

Hello,
I am using a Pixhawk RadioLink controller, and am having issues with receiving GPS.

When I check the Consol in QGroundcontrol, I see the following error:

[E] at :0 - “serialnmea: No known GPS device found. Specify the COM port via QT_NMEA_SERIAL_PORT.”

I have two external GPS units, and both are giving me the same error. I have already checked the pinout, and both appear to be correct. Any thoughts?