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# In Invoicing > Awaiting Approval, why do I get an "invoice must be unique" error when approving to Xero?

This is usually an invoice number conflict between ServiceM8 and Xero. When approving invoices to Xero, the invoice number must be unique.

## Related resources

* [Resolving Xero invoice number conflicts](/help-center/servicem8-add-ons/xero/resolving-xero-invoice-number-conflicts)