A warning when the number and the customer match
If you save an invoice and another one already has the same number and the same customer, you see a warning. It is there to stop a duplicate before you treat it as final.
When the warning appears
When the number and the customer match another invoice on the account. It does not appear for a similar amount, or for the same customer with a different number.
- Same number.
- Same customer.
- It is a warning, not a deletion.
What you do with the warning
You check which of the two you want to keep. Sequential numbering is not fixed by ignoring the clash. Reusing a number already used with that customer is the case the warning points at. The series is explained in invoicing software for autónomos.
Common questions
Does the warning delete the repeated invoice?
No. It points out that another invoice already has the same number and the same customer. You decide whether to delete or correct.
Does it warn if only the customer matches?
No. It needs the same number and the same customer together.
Official sources
Informational text reviewed on 26 September 2026. It is not tax advice and does not replace the Spanish Tax Agency or your accountant. Deadlines, rates, and forms can change.