How to document an unpaid invoice under a written contract in Canada

If you need to document an unpaid invoice made under a written contract, the most important steps are simple and evidence-focused: keep the signed contract and original invoice, collect contemporaneous proof the goods or services were delivered and accepted, send a clear written demand and preserve proof it was received, and—if you must litigate—organize those materials into a chronological evidence bundle that follows your province's small-claims rules and limitation periods.

Those steps matter because Canadian courts give decisive weight to documents created at the time of the transaction (contracts, invoices, delivery receipts, photos, and emails). If you act now you preserve the records that make an unpaid invoice a straightforward "liquidated" claim; wait and rely on reconstructed documents and you weaken your position.

What documents actually prove an unpaid invoice under a written contract

Start by separating three categories of evidence: (1) the contract and invoice, (2) proof of performance or delivery, and (3) contemporaneous communications about payment.

• Contract and invoice: Keep the signed written contract or any written confirmation that sets scope, price and payment terms, and the original invoice showing the amount, invoice date and stated terms. Courts treat an invoice under a written contract as primary documentary evidence—especially in small-claims court contexts. See Ontario's guidance on preparing evidence for Small Claims Court for how such documents are used in practice (Ontario Small Claims — Getting ready for court).

• Proof of delivery or acceptance: Delivery receipts, signed work-acceptance forms, time sheets, site photos with timestamps, shipping tracking records, or client emails acknowledging completion all show you performed. Contemporaneous proof is stronger than statements created after payment became overdue.

• Payment communications: Save emails, text messages, and any notes from phone calls that mention payment dates, disputes, or instructions (for example, a purchaser saying "we'll pay by X date"). Preserve metadata (timestamps) for electronic files where possible.

Why this matters: if the other party claims non-performance or a set-off, you will need contemporaneous documents to rebut that. Courts prefer original or contemporaneous records; invoices or summaries drafted only when you decide to sue are less persuasive.

How to issue and preserve an effective written demand (and why it helps)

A written demand (sometimes called a dunning letter) is not legally required in every case, but it serves three practical purposes: it gives the debtor a clear final opportunity to pay, creates a record that you attempted resolution before suing, and can be served in a manner that creates proof of receipt.

A useful demand letter should: restate the contract and invoice (dates and amounts), summarize the work delivered, quote the payment terms from the contract or invoice (for example, "30 days from invoice date"), attach the invoice and delivery proof, and set a short firm deadline for payment (commonly 7–14 days for business debts). Keep documentary proof of delivery: registered mail receipts, courier tracking, or an email read/received indicator.

The federal guidance on payment/demand content highlights that clarity about the amount and supporting documentation improves the chance of a commercial resolution; save the demand and any reply as part of your file (federal guidance on demands for payment).

Caveat: a demand letter does not by itself create or prove the debt—your underlying contract, invoice and proof of performance do that. But a well-documented demand can remove ambiguity, expose genuine disputes early, and create a record useful in court.

Preparing for litigation: organization, forms and limitation periods

If a demand does not produce payment, prepare an evidence bundle using the contemporaneous documents above. Organize evidence chronologically, include an index, and mark the contract, the invoice, and the clearest proof of delivery or acceptance. Small-claims courts expect parties to bring clear documentary evidence and a short summary of their claim; Ontario's Small Claims Court guide explains how to prepare and what to expect in court (Ontario — Making a claim).

Follow the exact filing and service rules for your province. For example, British Columbia uses a Notice of Claim (Form 1) with specific fields for where the contract was made and the amount owing (BC Notice of Claim — Form 1). In Ontario, you must file appropriate small-claims forms and later file an Affidavit of Service to prove the defendant was served (Ontario — Serving documents).

Limitation periods are critical. Most provinces run a two-year basic limitation period from the date the claim is discovered; British Columbia and Ontario apply this discoverability rule and BC also has a 15‑year ultimate limitation in some cases. Do not assume the same deadline applies everywhere—check the applicable provincial Limitations Act—Ontario's Limitations Act, 2002 is an example of the discoverability rule in statute (Ontario — Limitations Act, 2002). If you are near the limitation period, obtain legal advice promptly because a missed limitation can permanently bar your claim.

Practical example and tactical choices

Imagine you supplied CAD 12,000 of custom software to a Toronto client in March, invoiced March 31 with payment terms "net 30," and have the signed contract, project-acceptance email dated April 5, and the original invoice. Payment is overdue by 60 days and the client says they won't pay until a minor bug is fixed. Your practical options are: issue a written demand attaching the contract, invoice and acceptance email and give a 10–14 day deadline; begin a mediated settlement conversation with the acceptance email as leverage; or, if the client refuses, file in Small Claims Court (Ontario limit CAD 35,000) while ensuring you comply with Ontario filing and service rules and the two-year limitation (Ontario Small Claims guidance). The acceptance email materially strengthens your position because it is contemporaneous evidence of performance.

When to get professional help and a practical next step

If the dispute involves complex contract terms, counterclaims, amounts near or above provincial small-claims limits, cross-border elements, or an imminent limitation deadline, consult a lawyer. For many straightforward unpaid invoices, a properly documented demand letter and an organized evidence bundle are sufficient to secure payment or, failing that, to start a clean small‑claims action.

If you want a professional demand prepared from your information, consider a service that drafts a clear, evidence-based demand letter while keeping you in control. For example, prepares dispute documents from customer-provided information; customers decide whether and how to send those documents.

A well-documented file—signed contract, original invoice, contemporaneous proof of delivery/acceptance, preserved communications, a dated written demand, and compliance with provincial filing rules—gives your business the best chance of collecting an unpaid invoice or, if needed, winning a small-claims action. Act promptly so limitation periods and fading evidence do not limit your options.

For help preparing a professional dispute document, BeforeSuit can help you prepare your next steps.