Your customer calls and says "I paid my fines online and it charged my card twice." Actually the system is built to prevent double payments. Here's what happens.
If they used a bank debit card, the bank can place a hold on the funds in their bank account. This ensures the money will be there when the transaction is finally processed. Usually there's just a single hold on the funds. But if somehow the customer clicks the Submit button twice very quickly, there may be two holds for the same amount on the funds in their account. Eventually both of these holds will be removed when the funds are actually taken from the customers bank account. There is no way for the Library to release that extra hold on the funds. The bank places that hold and only they can clear it.
If the customer waits a few more days the second pre-authorization should go away. If they dispute the second charge the bank is likely to confuse it with the real charge and take the real payment away from us and charge us $20, which will get charged back to the library. So see if the customer can wait a few more days.
But what if they hit the back button during the transaction? The transaction that actually charges the credit/debit card only takes place after the Horizon fines are cleared. Even if a patron hits the back button after paying, it will not post a second charge to the credit/debit card because the specific fines have already been cleared.
On The Horizon is an FAQ publication for the staff of the Fresno County Public Library on the use of Horizon and ValleyCat.
