@Bill-Duet-3D you may way to update the firmware first.
grab these files and put it in a folder called firmware on the SD card
https://github.com/Duet3D/RepRapFirmware/releases/download/3.5.1/Duet2CombinedFirmware.bin
https://github.com/Duet3D/RepRapFirmware/releases/download/3.5.1/Duet2_SDiap32_WiFiEth.bin
https://github.com/Duet3D/RepRapFirmware/releases/download/3.5.1/DuetWiFiServer.bin
and extract this zip to the www folder
https://github.com/Duet3D/RepRapFirmware/releases/download/3.5.1/DuetWebControl-SD.zip
the run M997 and M997 S1 via terminal to update everything
then try adding your wifi details again
if it still doesn't work, grab a new M122