Look closely at what the principle actually excludes, it is oral evidence of the terms of a written contract, meaning the negotiated obligations the parties agreed to. It is not a blanket rule against oral evidence for every fact connected to a transaction that happens to have some paper attached to it.
A receipt is different from a contract in this sense, it is a written acknowledgment that a payment already took place, not a document laying out ongoing contractual terms that the parties are bound by going forward. Proving that a payment occurred is proving a plain fact, and that fact can still be established through oral testimony, the receipt being one way to prove it but not the only way.
Because the exclusion in the principle is tied specifically to contractual terms, stretching it to cover every receipt or acknowledgment would go beyond what the rule says, while removing the exclusion entirely would also go too far the other way. The narrower, accurate reading is that oral evidence to prove the fact of payment remains open here.
So the correct answer is Oral evidence to prove payment is allowed.
Asking what the receipt would need to be for each option to be correct isolates the answer.
Since the receipt is already a record of a completed fact rather than a set of contractual terms, and the other three options depend on a fact pattern that does not exist here, oral evidence to prove payment remains open.
Therefore, the correct answer is Oral evidence to prove payment is allowed.