Step one: decide whether you are owed, not just angry
Before you write a word, gather three things: the signed agreement or written scope, the invoice with its due date, and the proof the work was delivered. If any of the three is missing, the letter still works, but the missing one is where a dispute will live. Honest rule: if you cannot show what was delivered and when, you cannot win the argument later, in court or on a platform. Build the proof first, then write the letter.
The seven parts of a demand letter that holds up
- Who it is to. Name the person or company that engaged you, and reference the agreement date.
- The invoice. Invoice number, issue date, due date, exact amount, and the currency.
- The work summary. What was delivered, in plain list form, with dates.
- The evidence. Links, not attachments. One checkable record per deliverable. This is the section that decides everything.
- The deadline. A specific date, usually 7 to 14 days from sending, in writing.
- What follows. State your next step calmly: small claims, a platform dispute, collections. Name the forum, not the fury.
- Your signature and date. The letter is a record. Date everything.
The template
SUBJECT: Formal demand for payment, Invoice [NUMBER] Dear [Client name], On [date] we agreed [brief scope description]. Under that agreement I delivered the following, on the dates shown: 1. [Deliverable 1] - delivered [date] 2. [Deliverable 2] - delivered [date] Invoice [NUMBER] for [AMOUNT], issued [date], was due on [date]. As of today it is [N] days overdue. Evidence of delivery is attached below, as checkable records: - [Record link 1] - [Record link 2] I require payment in full of [AMOUNT] by [DEADLINE DATE]. If payment is not received by that date, I will pursue the matter further, including filing a claim in small claims court and disputing any platform reviews through the available process. Regards, [Your name], [date]
The bracketed fields are the entire job. Fill them honestly and the letter reads as business, not grievance. If you were paid a deposit, subtract it and show the arithmetic in the work summary.
The evidence section, done right
A demand letter with "see attached screenshots" loses to a demand letter with "check record 3". For AI-assisted work, the strongest evidence is a record saved when the work ran: the tool that ran, the time, the saved result. Each record sits at a public link you can paste into the template above. When the client opens one, they see the saved result and a way to check it, which is harder to dismiss than a chat export they can claim was edited. If your work produced receipts at zambo.dev/run, those links are the evidence section, one per deliverable.
If a scope change was agreed mid-project, put that agreement in the packet too: the date, who agreed, and what changed. Scope changes are the most common dispute trigger, and a dated record of the change ends them.
The deadline ladder
Send the letter by a channel you can prove delivery on, email at minimum. The usual ladder: 14 days in the first letter, 7 days in a follow-up if silence continues, then file. Keep copies of everything, including the "message seen" receipts. If the client replies with a partial story ("the work wasn't right"), answer with records, one disputed item per record, not with a debate. Courts and platforms both reward the person who brought the organized packet.
Honest limits
- This page is not legal advice and none of us are your lawyer. Small-claims thresholds and letter requirements differ by jurisdiction; check yours before you file.
- A demand letter does not make a weak claim strong. It organizes a strong claim. The proof comes first.
- A receipt proves the saved result was not changed. It never proves the work was good. Bring the deliverable quality too.
Questions, answered
How do I write a demand letter for an unpaid invoice?
Use a template with seven parts: the addressee, the invoice details, a work summary, checkable evidence links, a specific payment deadline of 7 to 14 days, your stated next step, and your dated signature. The evidence section decides the outcome: paste one verifiable record link per deliverable so a third party can check what was delivered and when.
What do I do if a client keeps delaying payment?
Move down the ladder in writing: a reminder, then a formal demand letter with a deadline, then file. Each step is dated and keeps a delivery trail. Never reopen negotiations on price after the letter goes out; answer new objections with records.
What evidence wins a dispute if I kept no records?
Less than you would want. Courts and platforms weigh dated, checkable records far above memory. The lesson is forward-looking: for every future job, save the record when the work runs, not after the dispute starts.