Welp, count me in the same group as
@staceyj2
Purchased a rental through UT with Budget, received the Budget confirmation number, but when I look up the reservation with Budget there's no where to enter my Fastbreak number. If I attempt to modify the reservation (only available to me via the app) I am immediately prompted that I'll be charged $200 for zero changes (and I should mention I can't add my fastbreak number on this screen either)
Now I have to decide if I want to risk waiting in line at the Budget counter, or pay significantly more and go with another rental company where I can skip the line..