The short answer: the core set is a contract or purchase order, the unpaid invoice(s), proof of delivery or acceptance, your account statements, and the correspondence about the balance. Together these answer the three questions any reviewer will ask: what was agreed, what was delivered, and what remains unpaid.
Collection work is an evidence exercise. The stronger and more complete your file, the fewer openings a debtor has to reopen settled questions — and the faster anyone reviewing the account can understand it. Here is the checklist, why each item matters, and how to assemble it.
The checklist
| Document | Why it matters | Priority |
|---|---|---|
| Contract, signed agreement, or purchase order | Establishes what was agreed: scope, price, payment terms, and who authorized it | Essential |
| Unpaid invoice(s) | States the amount claimed, the due date, and the invoice reference the debtor can match | Essential |
| Account statement / aging | Shows the balance over time and that the invoice remains unpaid | Essential |
| Proof of delivery or acceptance | Confirms the goods shipped, the service was performed, or the work was accepted | Essential |
| Correspondence about the balance | Records reminders, promises to pay, and any objections the debtor raised | High |
| Change orders / approvals | Covers scope additions that explain differences from the original agreement | High when applicable |
| Time records or milestone confirmations | Supports the "work was performed" side of service disputes | High for services |
| Prior payment history | Shows a pattern of paying — or not — and offsets any partial payments | Useful |
How the documents work together
Think of the file as a chain. The contract says what should happen. The invoice says what you billed. Proof of delivery says you held up your side. The statement says what is still owed. The correspondence says what happened after the due date. If one link is missing, the debtor's easiest defense is to point at the gap.
Preparing the file: a practical sequence
- Gather the agreement. Contract, SOW, or PO — including any amendments and who signed them.
- Export the invoices and statement. A clean statement showing invoices, dates, payments, and balance is easier to read than scattered PDFs.
- Add delivery or acceptance proof. Shipping documents, signed delivery receipts, sign-off emails, timesheets with client acknowledgment.
- Assemble the communication trail. Reminder emails, call notes, promise-to-pay messages, and any dispute the debtor raised — in date order.
- Flag the weak spots honestly. Missing signature? Verbal change order? Write it down now so it can be addressed before the debtor raises it.
Common gaps and how to close them
Verbal approvals
If scope changed through a phone call, reconstruct it: send a short email after the call summarizing what was agreed and ask for confirmation. Contemporaneous written confirmation is far stronger than a recollection months later.
Missing purchase orders
Many disputes dissolve when the PO number appears on the invoice and matches the buyer's system. Ask for it early — it is often the actual blocker inside the debtor's accounts-payable queue.
Partial payments
Apply every partial payment to the statement and recalculate the balance. An unexplained reduction in the amount you are claiming undermines confidence in the whole file.
What you should not send
Keep the file to what proves the debt. Internal notes that speculate about the debtor's finances, unrelated disputes, or sensitive personal data about individuals at either company do not belong in a collection file and can create problems of their own.
Next steps
Once the file is assembled, the question becomes timing: is this the moment to involve a third party? Our guide on when to send a business debt to collections provides the decision framework — and if you are ready to have an account reviewed, you can submit it through our contact page.