What Evidence Do You Need for an Unpaid Invoice Claim?

An unpaid invoice claim lives or dies on evidence. Australian tribunals and courts follow a simple test: on the balance of probabilities, did the claimant prove what they say happened?

For an unpaid invoice, that means three elements: the debt exists, you delivered what was agreed, and the debtor has no valid defence. This guide breaks down the minimum evidence required for each.

The three elements you must prove

Every unpaid invoice claim requires proof of:

1. The debt — that an agreement existed, the amount is certain, and payment was due
2. Performance — that you delivered the goods or completed the services as agreed
3. No valid defence — that the debtor has no legitimate reason to withhold payment

Miss any one of these and your claim fails.

Proving the debt exists

You must show that the other party agreed to pay you a specific amount for specific work or goods.

What counts as proof of agreement

Written contract or purchase order — the gold standard. A signed agreement, email acceptance, or approved purchase order establishes the terms, scope, and price without ambiguity.

Tax invoice — under Australian tax law, a compliant tax invoice is strong evidence of a debt. It must include your ABN, the date, a description of what was supplied, the amount payable including GST, and payment terms.

Email trail — if there is no formal contract, a chain of emails showing offer, acceptance, scope, and price will do. Tribunals accept electronic communications as binding agreements.

Quote accepted in writing — a written quote followed by “yes, go ahead” or “approved” creates an enforceable contract.

The amount must be certain

Tribunals will not enforce a claim for “about $5,000” or “roughly three days’ work”. The amount must be liquidated — a fixed, ascertainable sum.

If your invoice says “$4,500 + GST”, that is certain. If it says “time and materials to be confirmed”, that is not.

Payment terms matter

Your invoice should state when payment is due. Common terms include “Payment due within 7 days”, “Net 30 days from invoice date”, or “Payment on delivery”.

If no term was agreed, the law typically implies a reasonable time — usually 30 days. But stating it upfront removes any argument.

Proving you delivered

Proving the debt is not enough. You must prove you actually did the work or supplied the goods.

For goods supplied

Delivery docket or consignment note — signed by the recipient. This is the single best piece of evidence for physical goods.

Shipping receipt or tracking number — if sent by courier or post, the tracking record showing delivery to the correct address.

Photographic evidence — photos of the goods at the delivery location, timestamped if possible.

Email confirmation — “Thanks, goods received” or “All items arrived” from the buyer.

For services performed

Timesheets — dated records of hours worked, tasks completed, and who approved them.

Progress reports or completion certificates — documents showing milestones reached or the job finished.

Email updates — contemporaneous emails to the client describing what was done, when, and any issues encountered.

Before and after photos — for trades, landscaping, cleaning, or any visual work.

Client sign-off — an email or form where the client acknowledged the work was complete.

The substantial performance rule

Under Australian contract law, you do not need to prove perfect performance. If you completed the work to a reasonable standard and any defects are minor, you are still entitled to payment. The other party can counterclaim for the cost of fixing defects, but they cannot refuse to pay the entire invoice.

Proving no valid defence

The debtor will often claim a reason for non-payment. Your evidence must show their excuse is not valid.

Common defences and how to counter them

“The work was defective” — if they claim poor quality, you need evidence the work met the agreed standard. Photos, third-party inspections, compliance certificates, or an email from the client saying “looks good” before the dispute started.

“You didn’t deliver everything” — your delivery docket, packing list, or itemised invoice showing exactly what was supplied. If they signed for it, even better.

“We never agreed to that price” — your written quote, purchase order, or email acceptance showing the price was agreed before work began.

“You took too long” — if there was no agreed timeframe, the law typically implies a reasonable time. If there was a deadline, show it was met or that any delay was caused by the client (emails asking them for information, approvals they did not provide).

“We already paid” — ask for proof. If they cannot produce a bank statement or receipt, the defence fails.

“The invoice is wrong” — your invoice must be clear, itemised, and match what was agreed. If they dispute line items, your quote or contract should support each charge.

The burden shifts

Once you prove the debt and delivery, the burden shifts. The debtor must prove their defence. If they claim defects, they must show evidence of those defects. If they claim they paid, they must produce the receipt.

What format should your evidence be in?

Tribunals and courts accept evidence in multiple formats, but some are stronger than others.

Original documents — always better than copies. If you have the signed contract, bring it.

Electronic records — emails, PDFs, photos, and digital invoices are all admissible. Print them or save them as PDFs with metadata intact (date, time, sender).

Witness statements — if someone else saw the delivery, did the work with you, or heard the agreement, their written statement helps. Claim Done can prepare a witness statement in about 5 minutes if you need one.

Business records — your accounting software, CRM notes, or job management system can all be used to prove dates, amounts, and communications.

Third-party records — courier tracking, bank statements, or statutory declarations from suppliers or subcontractors.

How much evidence is enough?

You do not need a banker’s box full of paper. You need enough to prove the three elements on the balance of probabilities.

For a straightforward unpaid invoice claim, that usually means:

• One contract, quote, or purchase order
• One tax invoice
• One proof of delivery (docket, email, or photo)
• Any correspondence showing the debtor acknowledged the debt or the work

If the debtor raises a defence, you will need additional evidence to counter it. But start with the basics.

What if you do not have perfect evidence?

Not every tradie keeps signed delivery dockets. Not every consultant gets written sign-off. If your evidence is incomplete, you can still succeed — but you need to be strategic.

Reconstruct the timeline — use bank records, calendar entries, text messages, and any other contemporaneous records to build a picture of what happened.

Get a statutory declaration — if you delivered the goods yourself or did the work personally, swear a statutory declaration setting out the facts. It is not as strong as independent evidence, but it is better than nothing.

Use the debtor’s own words — if they sent you an email saying “thanks for the work” or “invoice received”, that is evidence they accepted delivery.

Get a witness statement — if someone else was there, get them to put it in writing. Claim Done can prepare a formal witness statement citing the relevant evidence rules.

The weaker your evidence, the more important it is to get your documents right. A well-drafted letter of demand or tribunal application can frame incomplete evidence in the strongest possible light.

How Claim Done helps with unpaid invoice claims

Claim Done’s Programmatic Algorithms work from your answers and draft the documents you need to recover the debt.

Letter of Demand — tell us about your invoice, delivery proof, and any correspondence. Our Programmatic Algorithms draft a letter citing the Australian Consumer Law and relevant contract law principles — and deliver it by email for $49.

Tribunal Application — if the debtor ignores the letter, we prepare your tribunal application and a witness statement. You attach your own evidence and lodge it with your state’s tribunal or court yourself.

Witness Statement — if you need a formal statement from yourself or someone else, we prepare it for you to check and sign (in New South Wales, an outline you complete in your own words).

Statutory Demand — if the debtor is a company and the debt exceeds $4,000, we prepare the statutory demand and supporting affidavit under the Corporations Act.

Every document is generated in about 5 minutes, flat fee, no subscription. You tell us about the evidence, we handle the legal formatting.

Final checklist: evidence for unpaid invoice claims

Before you send a letter of demand or file a tribunal application, confirm you have:

• [ ] Written agreement, quote, or purchase order showing the price and scope
• [ ] Tax invoice with your ABN, GST, and payment terms
• [ ] Proof of delivery (docket, email, photo, or tracking)
• [ ] Any correspondence showing the debtor acknowledged the debt
• [ ] Evidence countering any defence they have raised (if applicable)

If you have all five, your claim is strong. If you are missing one or two, you can still proceed — but get your documents drafted carefully to work around the gaps.

Unpaid invoices are one of the most common disputes in Australia. The evidence rules are not complicated, but they are strict. Prove the debt, prove the delivery, and prove there is no valid reason for non-payment. Claim Done prepares the documents you need to turn that evidence into recovery — starting with a letter of demand that is drafted in about 5 minutes and sent once you approve it.

Frequently Asked Questions

Do I need a signed contract to prove an unpaid invoice?

No. A signed contract is the strongest evidence, but Australian law recognises verbal agreements, email acceptances, and even conduct as binding. If you have a tax invoice, a quote the client approved, or an email trail showing agreement on price and scope, that is usually enough.

What if the debtor claims the work was defective?

They must prove the defects exist and that they are serious enough to justify non-payment. You counter this with photos, email sign-offs, or third-party inspections showing the work met the agreed standard. Minor defects do not void the entire invoice — they can claim the cost of fixing the defect, but they still owe you the rest.

Can I use text messages as evidence in an unpaid invoice claim?

Yes. Text messages, WhatsApp chats, and other electronic communications are admissible evidence in Australian tribunals and courts. Save them as screenshots with the date and time visible, or export them as PDFs. They are particularly useful for proving delivery, acknowledgment of debt, or the client’s acceptance of the work.

What if I lost the delivery docket?

You can still prove delivery using courier tracking records, emails from the client acknowledging receipt, photos of the goods at the delivery location, or a statutory declaration from yourself or a witness. A missing docket weakens your case slightly, but it is not fatal if you have other evidence.

How far back can I claim an unpaid invoice?

In most Australian states, the limitation period for a simple debt claim is six years from the date payment was due. After that, the claim is typically statute-barred and cannot be enforced. If your invoice is approaching the six-year mark, act immediately.