An invoice can be 45 days overdue and still not tell you what problem you actually have.

The customer may genuinely be short of cash. It may dispute the quality of the goods. Its accounts-payable system may be waiting for a missing purchase-order reference. The buyer may be asserting set-off. The debtor may be approaching insolvency. The payment may have been sent to the wrong bank account. Or the contract may never have made the invoice due on the date your spreadsheet assumes.

The first rule of payment-default work is therefore counterintuitive:

Do not start with collection pressure. Start by classifying the default.

That classification determines whether the next move should be an administrative fix, evidence exchange, commercial negotiation, lawyer's demand, arbitration, court claim, insolvency response or fraud/banking escalation.

Four numbers to write down before sending anything

Put these at the top of the file:

  • principal amount claimed;
  • contractual due date you rely on;
  • number of days overdue;
  • amount the debtor expressly admits, if any.

If the buyer admits USD 72,000 of a USD 100,000 invoice but disputes USD 28,000, you do not have one undifferentiated “USD 100,000 debt problem.”

You have an admitted-payment problem and a disputed-balance problem.

That distinction can change negotiation, evidence and procedure.

Problem type 1: administrative non-payment

Typical signs:

  • invoice never reached the correct AP address;
  • PO number missing;
  • tax or customs document missing;
  • supplier onboarding incomplete;
  • bank details changed and triggered verification;
  • internal approval stuck with one manager.

This is the cheapest problem to solve.

The better first move is often a documented AP reconciliation call, not a threatening legal letter.

Ask:

  1. Is the invoice in the buyer's system?
  2. Is it approved?
  3. What exactly is blocking release?
  4. Who owns the blocker?
  5. What is the promised payment run?

Then confirm the answer in writing.

Problem type 2: genuine commercial dispute

The buyer says the invoice is not payable because of quality, quantity, late delivery, defective documents, pricing, warranty, credit note, returned goods, set-off or counterclaim.

Now the question is not “Why haven't they paid?” It is which contractual condition to payment is disputed, and what evidence resolves it?

Build a mini issue table:

Issue Seller position Buyer position Evidence
Quantity 10,000 delivered 9,760 accepted signed receipt + warehouse count
Price USD 4.80 USD 4.50 agreed PO + later email
Quality within spec Lot 3 failed inspection report
Set-off none allowed USD 12k credit contract clause + credit correspondence

The dispute becomes manageable when each row has a source.

Problem type 3: liquidity default

The debtor does not seriously dispute the invoice but keeps asking for time.

Signals:

  • repeated promises without payment;
  • request to split the debt;
  • senior management suddenly involved;
  • suppliers asking each other whether anyone has been paid;
  • buyer offers a small payment “to show good faith”;
  • request for a long extension without new security.

Do not confuse cooperation with solvency.

A payment plan can be sensible, but it should answer the exact schedule, currency, interest or fees if applicable, what happens on one missed instalment, security or guarantee if commercially available and lawful, whether claims are reserved, and what legal step is paused and for how long.

Local insolvency law matters before applying aggressive pressure or accepting preference-sensitive payments.

Problem type 4: strategic withholding

Sometimes a strong buyer uses payment timing as leverage in a wider negotiation.

That does not automatically make the buyer's position unlawful. It does mean the supplier should stop treating the matter as routine collections.

Preserve:

  • admitted amount;
  • disputed amount;
  • buyer's written reasons;
  • leverage the buyer wants;
  • contractual set-off language;
  • termination or suspension rights;
  • key deadlines.

A supplier that retaliates by stopping all future shipments without checking its own obligations can create a second breach.

Problem type 5: fraud, misdirection or bank-event problem

If the buyer says it paid but the seller never received funds, do not assume ordinary non-payment.

Check SWIFT or remittance details, beneficiary account, payment date and currency, bank reference, whether bank details were recently changed, and whether an email account may have been compromised.

Business-email-compromise scenarios require immediate bank and security escalation. They are not ordinary “send another reminder” matters.

When is payment legally “late”?

That depends on the contract and applicable law.

A business spreadsheet may say “Net 30,” but legal analysis may need the signed contract, invoice terms, delivery date, acceptance mechanism and any statutory regime.

The UK provides a useful jurisdiction-specific example. GOV.UK states that qualifying B2B late payments can carry statutory interest, and the Late Payment of Commercial Debts (Interest) Act 1998 creates statutory-interest rights for qualifying debts subject to its scope and contractual rules.

The EU Late Payment Directive 2011/7/EU provides a framework for commercial transactions within its scope, including interest and recovery-cost concepts implemented through Member State law. The European Commission's Payment Observatory says the Directive is under review, so current local implementation should be checked rather than assuming one EU-wide operational answer.

These are examples, not global rules.

International sales add another layer

For qualifying CISG transactions, Article 78 addresses interest on sums in arrears. But the Convention does not make every practical interest-rate question disappear; local law, contract terms and interpretive issues can still matter.

UNIDROIT's Principles of International Commercial Contracts also include provisions on monetary performance and interest for failure to pay money. The Principles can be influential or contractually relevant in appropriate settings, but they are not automatically binding law in every transaction.

The safe drafting habit is to state a clear payment date, currency, permitted deductions, dispute process and late-payment consequences instead of relying on background law to fill every gap.

Wrong move vs better move

Wrong: “Pay immediately or we sue” before confirming the debtor entity.
Better: verify contract party, invoice recipient and asset-bearing entity.

Wrong: add an interest number copied from the internet.
Better: identify the contractual or statutory legal basis first.

Wrong: accept “invoice disputed” as a complete answer.
Better: require the disputed line item, amount and evidence.

Wrong: stop supply automatically.
Better: check suspension or termination rights and operational consequences.

Wrong: accept a 12-month plan because any payment feels good.
Better: compare the plan against solvency risk, security, limitation and enforcement options.

The first seven days

Day 1: reconcile contract, invoice, delivery and payment ledger.
Day 2: confirm debtor's reason for non-payment in writing.
Day 3: split admitted and disputed amounts.
Day 4: collect evidence for each disputed item.
Day 5: model settlement or payment-plan options.
Day 6: check deadlines, dispute clause and asset or solvency signals.
Day 7: choose the escalation path.

The timeline is an operating model, not a legal deadline.

What to put in the first serious payment message

Keep it factual:

  • contract or order reference;
  • invoice;
  • amount;
  • due date;
  • payment history;
  • debtor's stated issue;
  • documents already provided;
  • specific action requested;
  • response date;
  • rights reserved where appropriate and counsel-approved.

Avoid emotional accusations. The letter may become evidence later.

Four questions that turn a vague “payment default” into a defined work item

1. What exact monetary obligation matured?

Do not start with the total on the aged-receivables report. Tie each amount to a contract, purchase order, invoice, milestone or delivery event. A buyer may admit one invoice and dispute another.

2. What event made payment due?

Possible triggers include invoice date, receipt of invoice, delivery, acceptance, completion of a milestone or the end of a stated credit period. Local statutes can also affect payment timing in defined settings. The answer must come from the governing documents and applicable rules, not from the accounting software’s default “due” field.

3. Is non-payment the breach, or is it a symptom of another dispute?

A buyer who alleges defects may be asserting contractual remedies, set-off or a counterclaim. That assertion may be weak, strong or irrelevant, but it changes the work from routine collection to a contested commercial claim.

4. What would count as resolution?

“Get paid” is too vague for management. Define whether the acceptable outcome is immediate full payment, a secured installment plan, a documented set-off, return of goods, settlement, judgment, award or insolvency claim.

A first-call script for finance and sales

Before outside counsel is asked to “chase the customer,” finance and sales should be able to answer, in one call:

  • What is the undisputed amount?
  • What is the oldest due date?
  • What has the customer said in writing?
  • Who at the customer can approve payment?
  • What commercial promise has already been made?
  • Is anyone still shipping on open credit?
  • Is there a dispute notice or reservation of rights?
  • Which contract controls?

This short internal discipline prevents the collection strategy from being undermined by a salesperson simultaneously promising more time or more product.

One more boundary: aging reports are management tools, not legal conclusions

An accounting system may label an invoice “90+ days overdue,” but that label does not establish the governing due date, waiver, set-off, limitation position or legal entitlement to interest. Keep the aging report, but reconcile it against the contract and source documents before using it in a formal claim.

Bottom line

“Overdue invoice” is a status, not a diagnosis.

Classify the default first: administrative, disputed, liquidity-driven, strategic, insolvency-related or fraud/banking. Then match the response to the problem, the contract and the jurisdiction.

The goal is not to send the angriest reminder. It is to turn a vague receivable into a fact pattern that can be paid, negotiated or enforced.

General commercial information only, not legal advice. Payment deadlines, interest, set-off, insolvency effects and enforcement remedies differ by contract and jurisdiction.

Related Reading

Sources and Jurisdiction Boundaries