Build a coherent chain
Link the agreement or order to delivery, acceptance, invoice, statement, reminders, replies, promises, disputes and payments.
Menu
Recovery evidence
Show the agreement, performance, invoice and response trail.
Evidence should explain why the amount became due and what happened afterwards. The relevant set depends on the transaction, but originals, dates and context matter more than an impressive file count.
Preserve authenticity
Keep original files and messages, avoid undocumented edits and record where each item came from.