A staff member spots an error in an invoice issued yesterday. They open it, fix the figure, reprint it, and hand it to the customer. A natural act, done in good faith — and the most common invoicing violation there is.
Because an issued invoice is a final document. It is neither edited nor deleted — it is corrected with another document linked to it. That document is a credit or debit note.
Why an Invoice Isn't Edited
Three overlapping reasons:
- The customer's copy differs from yours. They hold the original and you changed yours — so which copy is correct?
- The invoice entered your tax filing. Editing it retroactively makes the submitted return stop matching your books.
- Deleting breaks the sequence. A missing number in the series is the first thing questioned at audit.
Which is why sound systems block editing technically rather than by policy alone — because what can be done will eventually be done under pressure.
Credit Note: When?
Issued when the amount owed by the customer decreases:
- Goods returned in full or in part
- A discount granted after the invoice was issued
- An overstated price or quantity
- Full cancellation of the transaction
- A defect in goods or a shortfall in service
Debit Note: When?
Issued when the amount owed by the customer increases:
- An understated price or quantity
- A line or service omitted from the original invoice
- Additional charges agreed later (shipping, installation)
- Correcting a VAT rate applied lower than required
The debit note is used less and neglected more — many companies issue a separate new invoice instead, losing the link to the original and making the two transactions hard to explain later.
What the Note Must Carry
| Field | Why |
|---|---|
| Its type stated explicitly: credit or debit note | Distinguishes it from an invoice at audit |
| Its sequential number and date | A series independent of the invoice series |
| The original invoice number and date | The link that makes the correction traceable |
| The reason for issue | Return, discount, correction — with no reason the note becomes a question |
| The affected lines and their values | Not the total alone |
| The VAT effect | VAT is adjusted with the original, not after it |
The third field is the essence of the whole document. A note not linked to an original invoice number is a document floating in mid-air — it explains nothing and corrects nothing.
Its Effect on Your Numbers
A note isn't a slip sent to the customer — it is a transaction that changes three things:
- The customer balance decreases (credit) or increases (debit).
- Stock takes back the returned item if the note covers a return.
- VAT is adjusted in the return for the period the note was issued in.
The third point is widely missed: a note enters its own period's return, not the original invoice's period. Trying to "fix" an earlier return with a later note creates a difference that is hard to explain.
Blocking edits is one of the criteria in choosing invoicing software, and the note requirements under e-invoicing are covered in the tax invoice guide.
Three Practices That Prevent the Problem Entirely
- Train your team on one rule: no editing, no deleting — a note only. One rule everyone remembers beats a long policy.
- Make the system block editing technically rather than relying on compliance.
- Review notes monthly. A cluster around one item reveals a pricing or data-entry fault — the note is a symptom, not the disease.
Frequently Asked Questions
What is the difference between a credit and a debit note?
A credit note reduces the amount owed by the customer (returns, later discounts, overstatements); a debit note increases it (understatements, omitted lines, agreed additional charges). Both must link to the original invoice number.
Can I edit an issued invoice?
No. An issued invoice is a final document held by the customer and entered in your tax return. Correction happens through a linked credit or debit note; editing or deleting breaks the sequence and makes your books indefensible.
What do I do if a transaction is cancelled entirely?
Issue a credit note for the full invoice value linked to its number, stating the reason for cancellation. Don't delete the original invoice — its presence in the record is what explains the note.
Which tax period does a note belong to?
The period in which the note itself was issued, not the original invoice's period. Which is why it should be issued as soon as the need appears rather than deferred to year end.
Does a note have its own numbering?
Yes, a series independent of the invoice series, with the original invoice number referenced inside the note. Mixing the two series confuses tracing at audit.
What does a high volume of credit notes indicate?
Usually a deeper problem: a recurring pricing error, items entered at outdated prices, or weak invoice review before issue. Treat the cause, not the effect.
Conclusion
An issued invoice isn't corrected with an eraser but with a document. And the difference between two companies isn't the number of errors — it is that one documents its corrections and the other hides them without meaning to.
Ask whoever issues your invoices one question: what do you do when you find an error in yesterday's invoice? The answer tells you whether you are protected.