This would also solve a major annoyance I have with card payments, which is no way to link a particular purchase back to a transaction.

With checks, you write a check and can write down the check number with a note about what the payment was for. When the payment posts, the check number is part of the transaction. With a card payment, they charge your card and, sometimes days later, there's a pre-authorization with some obscure transaction description. So many scary transaction descriptions that make me think "wait is this fraud".

With this method, the approval flow would also allow people to add a blurb for what the transaction is for.