Your client says the file never arrived. An API can settle that now.
The argument is always the same. You sent the work on Tuesday. The client says the folder was empty, or the version was wrong, or nothing showed up at all. There's no referee. Just two inboxes and a payment sitting in the middle. ProofReceipt fixes the receipt side of that. When you deliver, the app hashes the file with SHA-256 and gives you a receipt that ties that exact file to that moment. Change one character in the file and the hash changes. That's the whole trick, and it holds up because…