For POP entries, the Originator must void the source document (check) and give it back to the Receiver, but they are still required to obtain authorization and retain it for two years. Under NACHA rules, you can write to the Originating bank (ODFI) and request copies of the authorizations, and they must provide you a copy within 10 banking days.
You can find information about POP entries starting on page OG202 of the 2014 NACHA Rule book. Your payment Association should be able to answer additional questions about it, including warranty claims. Ours (WesPay) has an excellant Hotline.
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