This is one of many ways Budget sucks .... they will deduct the coupon at the desk .... sometimes .... as although you must enter the coupon for the reservation, the reservation system won't tell you if it will apply (or not) and/or what the discount will be.

More than once, I have had what I thought was a valid coupon refused at the desk. The last time was over a year ago and I haven't used Budget since. I probably never will (if I am counting on a coupon) until they change to match what everyone else does .... that is to validate (or reject) the coupon at reservation time, show the discount, and guarantee it's validity.