You can find all of your notification requirements in Reg E 205.11
First, your are required to notify your customer of provisional credit. Informs the consumer, within two business days after the provisional crediting, of the amount and date of the provisional crediting and gives the consumer full use of the funds during the investigation
Note that this notification need not be in writing. However, from an audit/compliance standpoint it is important that you be able to document customer notification. I find that having dated letter is the easiest way to do this, but you have the option of making an oral notification and documenting the date/time/method, in your dispute file. One you reach a final decision, again there is a notification requirement. Reports the results to the consumer within three business days after completing its investigation (including, if applicable, notice that a provisional credit has been made final).
If you are finalizing the provisional credit or issuing final credit, again this notificaiton can be oral provided that you document your compliance. If you are denying the claim and/or revoking the provisional credit, then the notificaiton must be in writing. (d) Procedures if financial institution determines no error or different error occurred. In addition to following the procedures specified in paragraph (c) of this section, the financial institution shall follow the procedures set forth in this paragraph (d) if it determines that no error occurred or that an error occurred in a manner or amount different from that described by the consumer:
(1) Written explanation. The institution's report of the results of its investigation shall include a written explanation of the institution's findings and shall note the consumer's right to request the documents that the institution relied on in making its determination. Upon request, the institution shall promptly provide copies of the documents.
(2) Debiting provisional credit. Upon debiting a provisionally credited amount, the financial institution shall:
(i) Notify the consumer of the date and amount of the debiting;
(ii) Notify the consumer that the institution will honor checks, drafts, or similar instruments payable to third parties and preauthorized transfers from the consumer's account (without charge to the consumer as a result of an overdraft) for five business days after the notification. The institution shall honor items as specified in the notice, but need honor only items that it would have paid if the provisionally credited funds had not been debited.
I hope this helps clarify the regulatory requirements.
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