If a US or UK client stops paying, escalate in this order: pause work → formal written demand letter with a deadline → the platform's or payment processor's dispute process → online dispute resolution (ODR) or mediation → small claims court, only if the amount justifies the cost of winning. Skipping straight to threats or lawsuits usually costs more than it recovers; working the sequence in order gets the highest share of freelancers paid fastest.
The moment an invoice goes overdue, pause any further deliverables — continuing to work for a non-paying client just grows the unpaid balance. Pull together the signed contract or scope agreement, all invoices, delivery confirmations, and the email/chat thread showing the client accepted the work. This paper trail is what makes every later step (demand letter, platform dispute, court filing) credible.
A demand letter (or "letter of demand") is the last step before you escalate to a platform, agency, or court, and it should be short, specific, and unemotional — vague letters get ignored, precise ones get paid. Include: both parties' full legal names, every unpaid invoice number/date/amount, the total owed, payment instructions, a firm deadline (7–14 days is standard, shorter if the invoice is already very late and reminders were ignored), and what happens if the deadline passes. Send it by email and, for larger amounts, also by a method that proves delivery (Paidnice's letter of demand guide).
If you were paid through Upwork, Fiverr, or a similar marketplace with escrow, use their dispute system before anything else — funds are usually already held or protected. On Upwork, filing a dispute forces the client to respond within five calendar days or the escrow releases to you automatically; a disputes specialist then issues a non-binding recommendation, and unresolved cases can go to binding arbitration (Upwork's dispute process; Fixed-Price Payment Protection). If you invoiced directly via Payoneer, Wise, or bank transfer with no escrow, there's no built-in recovery mechanism — this is exactly why the contract clause in Step 6 matters (Payoneer: what to do if a client doesn't pay).
For direct contracts, ODR platforms (like the American Arbitration Association's ODR service) let both sides resolve a payment dispute remotely through structured negotiation, mediation, or arbitration — faster and cheaper than a courtroom, and increasingly used for cross-border freelance invoices (AAA ODR; online arbitration for freelancers).
In England and Wales, small claims covers debts up to £10,000, and a UK address isn't required to sue a foreign company — you serve papers overseas using paper form N1 plus N510 instead of the online Money Claim service (Experi's UK small claims guide; UK Business Forums thread). In the US, limits and rules vary by state. The real constraint is enforcement: winning a judgment against a client with no local assets often costs more in legal fees and travel than the invoice is worth, so reserve court for larger amounts.
Before the next project, your contract needs a clause specifying: governing law (whose country's law applies), a staged process — negotiate, then mediate, then arbitrate or litigate — and, ideally, a named arbitration body so a stalled dispute doesn't default to an expensive foreign court (fynk's dispute resolution clause guide; contract clauses that protect a Nigerian freelancer).
Require a deposit or milestone payments so no single unpaid invoice represents 100% of the work, and keep a simple calendar of invoice due dates so a slipping payment gets a reminder — and a demand letter — before it goes cold.