When the system tried processing a newly entered ACH account for auto pay, it returned "Returned (R04: Invalid Account Number)." The family is confident they entered the correct account information.
Please have the family ask their bank about this. Some banks do not allow an automatic ACH withdrawal without the bank granting permission. If the account number was entered correctly the bank would be able to tell if a transaction was attempted or not. Once the bank has granted permission then auto pay should go through the next month without needing to do anything else.
If the bank did not see any transaction attempts on that account then the family most likely entered some information incorrectly.