ACH payments can't just be reversed for any reason, only for duplicate payments. Also, they can send a request, but if the funds are not in the account you are not required to honor the return. Your bank is not at risk unless you fail to follow the NACHA rules correctly. However, in all cases, if the funds are not available you would return the debit entry within the correct timeline. Failure to do so is when you put yourself at risk.
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