Hello, @dave_thompson.
Currently, there isn't an option in place to warn if a duplicate customer invoice number is used in QuickBooks Self-Employed if you manually enter them. The invoices in QuickBooks Self-Employed are for tracking purposes only and they don't affect your business and tax reports.
For now, you can manually track the invoice transactions and edit the invoice number. To do so, please refer to these steps:
- Go to the Invoices menu.
- Look for the Invoice you need to edit, click it and select Edit Invoice.
- In the Invoice no. box enter the correct invoice number.
- Click Save as draft or Send invoice.
I’m also adding an article that provides an overview of the Invoice feature. It includes instructions on how to customize the sales template, turn on the payments option, etc.: Create invoices in QuickBooks Self-Employed.
Also, when you receive the invoice payments, make sure to track them under the Transactions page. You can use this link for more information: Manually add transactions in QuickBooks Self-Employed.
In case you need to set your numbering preference, you can use the Custom transaction numbers feature in QuickBooks Online. This adds an Invoice no. field where you can enter any number or letter format you want and the sequence you set here applies to all sales forms: How to change the invoice number on sales forms.
If you have further questions about invoices in QBSE, please leave a reply below. I'll be always around to help. More power to your business.
