Yes, GPS data shows and time is set correctly, LEDs on QLG1 light up.It seems that for some reason the PPS is not reaching the U3S. If your meter has a bargraph it will show the pulses. Other ways an analogue meter or scope.
When you suggest having a receiver to monitor
transmissions, do you mean to see if I hear the signal at the frequency I've selected?Yes, if you send the audio to WSJT-X you can receive WSPR from others. Once you have done that then remove the antenna and check your own transmissions.
Your settings seem OK to me.
73 Alan G4ZFQ
Here are my settings: