Why is my client randomly getting Duplicates of invoice numbers? is there a way to stop this from happening?

Hello andrew-better-bo,

Thanks for posting in the Community!

Here's how to check your invoices and invoice numbers if there are duplicates or not. 

1. Click on the Sales tab.
2. Select the No. column to sort it.
3. When the Sales populate, it toggles the numbers in ascending and descending order.
4. Check for duplicates.

To prevent duplicate invoice numbers in the future, we can customize your Accounts & Settings preference. This feature is activated by default. If you do not want QuickBooks to automatically assign numbers to your sales forms, you can turn off this feature.

Here's how:

1. Click on the QuickBooks Gear icon.
2. Click on Account and Settings.
3. Click the Sales tab.
4. Click the Sales form content section.
5. Uncheck the Custom transaction numbers box.
6. Click Save, then Done.

Then, try to create a dummy invoice and use the next or last sequence number for your sales form. The system should sequence the next invoice number on your next invoice. 

Also, you can check this link to learn more about How to find duplicate invoice, quote, or sales receipt numbers.

Post again in the Community if you have more questions. The team is here to help you.