My client won't repay ad spend I paid on their behalf. How do I claim it?
The short answer
Like any unpaid invoice. Put the platform spend on its own line at exactly what you paid, with the client's written approval behind it, and chase it as a debt. Where the recharge is part of the price of a contract for services, interest at 8% over the Bank of England base rate5 and a fixed sum of £40 to £100, by invoice size4 usually apply too. If your name is on the platform account, it bills you whether or not your client pays, so claim early.
England and Wales only. WolfX is software, not a law firm.
What you can add
£6,250 of ad spend, 78 days late
Say you ran a client's campaigns in June 2026 and paid the platforms £6,250 on your own card. You invoiced £7,250 on 30 June 2026 on 14-day terms: the spend at cost plus a £1,000 management fee. It fell due on 14 July 2026. On 30 September 2026 it is still unpaid: 78 days late. It went late in July, so the rate for 1 July to 31 December 2026 applies: 8% plus the Bank Rate of 3.75% on 30 June, which is 11.75%7.
- Platform spend, at exact cost£6,250.00
- Management fee£1,000.00
- Interest: £7,250 × 11.75% ÷ 365 × 78 days6£182.04
- Fixed sum (invoices from £1,000 to £9,999.99)4£70.00
- Owed on 30 September 2026£7,502.04
Until they pay, it grows by £2.33 a day. All through those 78 days the platforms were paid from your card, not theirs.
The road ahead
Seven steps. All free.
Step 1: Work out who owes whom
Read your own account terms. If your name is on the platform account, you owe the platform on those terms, and your client owes you under your agreement. Their not paying does not cancel your platform bill.
Step 2: Build the proof pack
Gather the client's written approval of the budget, the platform statements for the period, and an invoice with the spend on its own line at exact cost and your management fee on another. A mark-up hidden in the spend line is the quickest way to lose the argument.
Step 3: Check how HMRC classes the spend
HMRC treats a payment to a third party as a disbursement1 only if all of these hold: you acted as your client's agent; they received and used the service; they were responsible for paying; they authorised you; they knew a third party would supply it; you itemise the outlay; you recover only the exact amount; and it is clearly additional to what you supply yourself.
That is a VAT test, not contract law. If the platform account is in your name, paying it was your responsibility, so the spend usually fails. HMRC then calls it a recharge, and a VAT-registered business charges VAT on it2. How to treat VAT on the invoice is for your accountant.
Step 4: Send the claim in writing
Email the letter below at about day 14 late, with the approval and statements attached. Interest and the fixed sum usually apply where the recharge is part of the price of a contract for services between two businesses3, so check your agreement reads that way.
Pause live campaigns only if your agreement has a clause that lets you: without one, stopping can put you in breach. With one, give the notice it asks for, with a date.
Step 5: Split the disputed from the undisputed
If they say the campaign underperformed, that is a complaint about your service, not about whether the platforms were paid. Ask in writing which part they dispute, and ask for the rest now. Keep the unpaid sum on its own invoice, and do not fold it into next month's fees without telling them in writing.
Step 7: Change the next agreement
Set a monthly spend cap, take a deposit or payment in advance, or have the client pay the platform direct. Get each month's budget approved in writing.
A letter you can copy
Letter claiming unpaid ad spend
Send it to the client's finance contact at about day 14 late, once a friendly reminder has not worked.
Tap a highlighted gap to see what goes in it.
Send it by email so it is dated, and keep a copy with the approval and statements. If your agreement sets its own fair late fee, use it in place of the interest and fixed sum. If it does not make the spend part of the price, work the interest on your fee alone; the fixed sum still applies, by the size of the fee.
When not to bother
When it isn't worth it
- The spend is small and the client is worth more. Ask once, in writing, and agree a payment date; a few hundred pounds rarely repays a lost client.
- The client is in liquidation or administration. A claim letter is the wrong tool; you prove your debt to the person running the company instead.
- There is no written approval and the campaign did poorly. Your position is weak, and a settlement for part of the sum may be worth more than a claim.
- The agreement was with another company. Check who signed it. The claim goes against the company named there, which may not be the one that used the ads.
- The client is in Scotland or Northern Ireland, or the debt is over six years old. Those two have their own court process10. In England and Wales a claim must usually start within six years9.
The Wolf's note
Two debts are running here, and the platform's does not wait for your client's. So the claim should not wait either: spend on its own line, approval attached, one date to pay.
Mr. Wolf · the AI inside WolfX
What comes next
Your next move
My client disputes my invoice. What happens next?
The disputed part waits.
6 min read · Letter included
What proof do I need to show I did the work and they owe me?
Proof is five kinds of paper: the deal, the work, their acceptance, your invoice and your chasing.
7 min read · Letter included
So it doesn't happen again
Should I ask for a deposit or payment upfront, and how do I ask?
Yes, when a job costs you money before the client pays, or the client is new.
7 min read · Letter included
Don't want to do this yourself?
The Wolf does every step for you. He works out the sums, writes the letters and keeps track of every date. Nothing goes without your yes.