LATAM context
The CEP is the document a vendor might ask you for to confirm you paid via SPEI. You download it from Banxico's portal by entering the tracking key, the CLABEs and the date. It's legally binding.
Concrete example
If you paid $50,000 MXN to a vendor via SPEI and they say they never received it, you generate the CEP at banxico.org.mx with the tracking key. If the CEP exists, the money left your bank and the responsibility shifts to the receiving bank.
How it shows up on your bank statement
The CEP itself doesn't appear inside the statement. It's a separate document you download from Banxico's portal. What the statement does carry is the SPEI tracking key, and that's the piece of data you need to issue one, along with the date, amount and receiving CLABE.
How does finO$ handle this?
finO$ extracts the SPEI tracking key from every transaction on your statement, so you can generate CEPs automatically or audit them in bulk.