I Need to Sue a Customer Who Won't Pay Their Invoice (Missouri)

The good news is that you usually have several theories to lean on, the deadlines are generous enough that you have time to do this right, and a firm demand letter alone often shakes the money loose without a courtroom ever entering the picture. This guide walks you from that first letter to a filed case, with an honest eye on getting paid at the end.

Start with a clear final demand letter

Before you file anything, send a written final demand. It is cheap, it creates a record, and it works more often than people expect — a formal letter signals you are serious, and many customers pay rather than risk a suit.

• State the basics plainly. Identify the invoice number, the amount owed, the work or goods provided, and a firm deadline to pay (say, 10 or 14 days).
• Reference your terms. If your contract or invoice provides for interest on late balances or attorney's fees, mention them — that raises the stakes for the customer.
• Make the statutory demand. Missouri allows prejudgment interest on a liquidated (fixed, calculable) demand once you make a proper written demand for payment (RSMo § 408.020). A clear dated demand letter can start that interest clock running.
• Keep proof. Send it so you can show delivery, and save a copy with the date.

A demand letter costs you almost nothing and resolves a large share of unpaid-invoice disputes on its own.

Know your claims — you usually have more than one

An unpaid invoice is rarely a one-theory case. Pleading alternatives protects you if one theory has a weak spot.

• Breach of contract. This is the core claim: there was an agreement (even an order confirmation or signed estimate), you performed, the customer didn't pay, and you were damaged. A written agreement is strongest, but Missouri enforces many oral and informal deals too.
• Account stated. If you sent statements or invoices showing a running balance and the customer received them without objecting, Missouri law may treat that agreed, unobjected-to balance as an account stated — essentially a new promise to pay the stated sum. Silence in the face of a clear bill can work in your favor.
• Quantum meruit. Where there's no clear contract — you did work at the customer's request without a signed deal — you can still recover the reasonable value of the goods or services the customer accepted. It's the fallback when the paperwork is thin.

You can plead these together, in the alternative, so a gap in one doesn't sink your whole case.

Pick the right Missouri court for the amount

Which court you file in depends mostly on how much you're owed. Missouri's trial courts are tiered, and the dollar thresholds change over time, so confirm the current limits with the circuit clerk or the court's website before you file.

• Small claims (associate circuit small-claims docket). For smaller balances, the small-claims docket is fast, simplified, and inexpensive. Procedures are streamlined, filing is cheap, and you often don't need a lawyer — it's designed for people to represent themselves. There is a dollar cap, so it only fits claims under the current limit.
• Associate circuit division. For mid-size amounts above the small-claims cap, cases go to the associate circuit division. It's more formal than small claims but generally faster and lighter on procedure than the full circuit court, which suits typical business-debt amounts.
• Circuit court. Larger claims belong in the circuit court, with full civil procedure, discovery, and the most formal process.

Filing in the wrong tier wastes time, so check the current thresholds rather than relying on a number you read somewhere — they get adjusted.

Add interest and fees where the law allows

You may be able to recover more than the face amount of the invoice — but only within limits Missouri sets.

• Prejudgment interest. On a liquidated demand — a sum that is fixed or readily calculable — Missouri allows statutory prejudgment interest after a proper written demand for payment (RSMo § 408.020), commonly 9%. This is one reason a clear, dated demand letter matters: it can start that interest accruing.
• Attorney's fees. Missouri follows the "American Rule," so each side normally pays its own attorney's fees. You can recover fees only if your contract or invoice terms provide for them, or a specific statute allows it. If your invoices or signed agreements include a prevailing-party or collection-fee clause, you may be able to add those fees — if they don't, you can't.
• The lesson for next time. If you're regularly chasing payment, build interest and attorney's-fee language into your standard invoice and contract terms going forward.

Don't let the deadline run

Missouri imposes strict statutes of limitations, and a claim filed late is usually barred no matter how clearly you're owed the money.

• Written contract. A written agreement to pay money generally carries a longer limitations period under RSMo § 516.110.
• Oral contract or open account. An unwritten agreement or an open account generally falls under the shorter period in RSMo § 516.120.

The clock typically starts when the breach occurs — usually when payment came due and wasn't made. When you're unsure which period applies, assume the shorter one and act accordingly. Don't sit on the debt waiting for the customer to "come around."

Plan for collection before you spend a cent

Here's the part most people skip, and it's the most important: a judgment is just a piece of paper until you collect it. A Missouri court can declare the customer owes you, but the court won't hand you the cash — you have to enforce the judgment through tools like wage or bank garnishment and judgment liens against property. If the customer has no job, no bank balance, and no reachable assets — what collectors bluntly call "judgment-proof" — you could win and still get nothing while spending real money on filing and effort.

So before you file, do a sober assessment:

• Is the customer solvent? A going business with revenue and bank accounts is collectible; one that's shutting down or broke may not be.
• Are there assets to reach? Wages, business receivables, bank accounts, and real estate all give a judgment something to bite.
• Is the amount worth the cost? Weigh filing fees, your time, and any attorney's fees against what you'll realistically recover.

If the customer is solid, suing makes sense. If they're insolvent, sometimes a partial settlement now beats an uncollectible judgment later.

Frequently Asked Questions