You’ve double-checked and confirmed that the station i.d. and password with which you registered at WU and what’s configured into your PWS match?
Hmmm… Searching on it (it’s been years since I’ve done PWS reporting to WU [I wrote my own code to do it, back then]), it would appear WU made an unannounced change to their PWS reporting protocol.
I would try searching on the make & model of your PWS, along with “weather underground” and the word “reporting”. See if anything shows up.