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

If a customer under a written contract hasn’t paid, the single best thing your business can do is assemble a short, convincing, time‑stamped record that links the contract to the invoice and to performance. That means keeping the written agreement (or a clear email exchange that shows the contract), the invoice showing date/terms (including required GST/HST details if you are registered), contemporaneous proof you delivered the goods or completed the work, and any communications or acknowledgements from the customer—then sending a dated demand and preserving proof of delivery before you consider court. The rest of this article explains which documents actually matter, how to preserve them so they’re admissible, what to say in a demand, and how provincial rules can change your timing.

What documentary evidence courts and small‑claims tribunals expect

Most Canadian civil forums look for a small, logical package of documents that proves (1) a contract existed, (2) you performed, (3) you invoiced, and (4) payment remains outstanding. Assemble these items first:

• The written contract or signed purchase order, or a clear email chain that establishes the agreement and price. If the contract states payment terms or an interest/late fee, include that page.

• The unpaid invoice(s) with invoice number, date, due date and the amount claimed. If your business is GST/HST registered, make sure your invoice includes the information the Canada Revenue Agency requires—this improves tax compliance and the clarity of your evidence (see the CRA guidance on invoices).

  See the CRA’s invoice requirements for details: Invoices (GST) — Canada Revenue Agency.

• Proof of delivery or performance: signed delivery receipts, completion or acceptance certificates, client sign‑offs, photographs with timestamps, project timesheets, shipping records or bills of lading.

• Payment‑related records: your accounting entries, bank deposit records, and any sent payment reminders or statements.

• All communications that acknowledge the debt or show dispute points: emails, text messages, or recorded telephone notes summarising conversations.

Why these items matter: business records created in the ordinary course (ledgers, invoices, shipment logs) are admissible under the Canada Evidence Act’s business‑records approach, but courts still require foundation and authenticity if the debtor disputes them. For the basic rules on business records and admissibility, see the Canada Evidence Act: Canada Evidence Act.

How to preserve and authenticate electronic and paper records

In practice, evidence problems arise when records are incomplete, altered, or lack provenance. Follow these practical steps:

• Keep originals where possible. If you work digitally, keep unedited copies and preserve system metadata or export logs; do not overwrite files.
• Maintain an audit trail: indicate who created the document, when, and where it was stored. A short custodian note explaining how records are generated and stored can be useful if the other side later disputes authenticity.
• Follow CRA retention rules as a baseline: the CRA’s guidance on record keeping recommends retaining business records for a minimum period (useful both for tax and evidence reasons). See: Keeping Records — Canada Revenue Agency.
• If a document’s authenticity may be challenged, plan for a witness (for example, the person who issued the invoice or managed the delivery) who can swear an affidavit or testify about the record’s creation and accuracy. Many courts accept properly supported business‑record affidavits, but local rules determine the exact format required.

If you rely on emails, preserve full headers and the complete thread rather than screenshots: a full export is easier to authenticate.

Demand letters: what to send, how to send it, and what a good demand proves

A concise, dated demand letter is a low‑cost, commonly recommended step before court. It does three things: it summarises the claim; it asks for payment by a specific date; and it creates a documented last‑chance attempt to resolve the dispute that you can show a judge or tribunal.

A useful demand letter should contain:

• A short statement of the contractual basis for the claim and the invoice number, date and amount.
• A summary of the performance you completed (for example, “installation completed and signed off on May 12, 2025”).
• A clear deadline for payment (for example, 14 days) and a statement that you reserve your rights to collect interest or file a claim if unpaid.
• A request for a written response if the debtor disputes the debt, identifying the specific basis for the dispute.

Proof of delivery matters. Use a method that creates a receipt or signature: registered mail, courier with a signature, or email to a monitored business address and keep the delivery receipt or the email delivery/read receipts. If you later file in court, you’ll want evidence that the debtor received the demand.

Short example (adapt to your facts):

Invoice demand (short)

Date: [date]

To: [Customer name]

Re: Invoice #[invoice no.], dated [date], amount $[amount]. Under our written agreement dated [contract date], we delivered [goods/services] on [date]. Payment became due on [due date] and remains unpaid. Please pay $[amount] within 14 days, or we will consider filing a claim.

A short, factual demand like this serves primarily to document the claim and the opportunity to resolve it. It does not establish legal entitlement by itself—if the debtor disputes the facts, the dispute will need evidence.

Timing and provincial differences you must check before suing

Limitation periods and the proper tribunal vary by province and by contract terms. Don’t assume a universal deadline.

• Ontario commonly uses a two‑year limitation period measured from discoverability, with other ultimate limits; for provincial guidance see the Ontario Limitations Act: Limitations Act, 2002 — Ontario. Ontario’s small‑claims procedures and expectations about documents and pre‑action communications are described in the government’s small‑claims guide: Guide to procedures in small claims court — Ontario. The Small Claims Court rules include a documentary‑evidence timing rule: see the Small Claims Court rules (O. Reg. 258/98): Rules of the Small Claims Court — Ontario.
• British Columbia operates different limitation mechanics; small claims and many low‑value disputes may go to the Civil Resolution Tribunal (CRT). For how small claims are handled in BC see the CRT: Civil Resolution Tribunal — BC and a description of limitation periods in BC materials: Limitation Periods — Clicklaw BC.
• Alberta’s court resources explain pre‑action considerations and the civil claims process; check the Alberta Courts’ “Before You Sue” guidance: Before You Sue — Alberta Courts.

Choice‑of‑law and forum clauses in the contract can change which province’s rules apply. If limitation periods are near expiry, preserve evidence of performance and any debtor acknowledgements—many provinces allow a written acknowledgement or part payment to restart the clock, but the rules differ.

If you need a quick sense of provincial law on prescription in civil law fora (Quebec), the Supreme Court and appellate decisions shape how prescription is applied in specific cases—consult your local rules and, if necessary, a lawyer; see an illustrative Supreme Court decision: Pellerin Savitz LLP v. Guindon — SCC.

Practical checklist before filing, and when to get counsel

Before you file a claim, confirm you have:

• The signed contract or equivalent, and the specific invoice(s).
• Delivery/performance proof tied to the invoice dates.
• Bank records showing non‑payment and any partial payments.
• Copies of the dated demand and proof of delivery.
• Notes of any debtor acknowledgements (email or signed notes).

Get legal advice if limitation periods are close; the contract contains complex forum/arbitration clauses; the debtor disputes ownership/assignment of the debt; or you expect enforcement steps (garnishment, writs) or insolvency concerns. Court procedures and evidence rules—such as how and when to serve documentary evidence—vary by forum and matter.

If you want a professional, polished demand letter and evidence checklist prepared from your documents, consider using a specialist drafting service that turns your supplied facts into a professional demand letter and delivery options: BeforeSuit's professional demand-letter preparation service. Using a service does not replace legal advice when rules or timelines are uncertain.

A final practical note: a clean, concise evidentiary package (contract → invoice → performance proof → demand) is much more persuasive — and more likely to be resolved without court — than multiple, inconsistent records. Start assembling the package today, note important dates (delivery, invoice, demand sent), and check the relevant provincial limitation and forum rules before you file.