Essentially, the regulation requires you to make the customer whole. That means that you reconstruct the account history without the unauthorized transaction or after adjusting for an error. If the customer would have earned more interest, you must pay it. If the customer would have avoided a fee (any fee) imposed by your bank, you must refund it.
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John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8