Keep the original agreement
Retain the version the client reviewed, the signature record, and the agreed scope. A file hash can show whether bytes changed; it does not establish who signed.
Capture delivery
Save delivery receipts and relevant client communication alongside the transaction. Include dates and context rather than a pile of unrelated screenshots.
Respond to the reason
Read the reason code and provider deadline. Explain how each relevant record addresses the claim. The issuer decides the result; no evidence package guarantees success.