This is the first time I have been informed by one of our clients that an extension payment we thought went through fine was never received by the IRS. How often does this happen with ProSeries?
Sounds like it has happened at least once.
Based on my own dealings with rocket scientists for clients, are you sure that you have the proper bank account information and are you sure that it really never came out of their account?
I feel like it might have happened once back a few years ago.
I try to never schedule a payment right on the due date, I always schedule them a few days prior, and tell the client to watch their account just in case it doesn't happen for some reason, we still have time to pay through the IRS website or get a check postmarked by the due date.