Hello there, Allan. I noticed it’s your first post, so I wanted to take a moment to welcome you to the Community. QuickBooks Desktop automatically assigns sequential transaction numbers based on your last saved entry. I'll ensure your team can prevent using similar details for accurate tracking with the information below.
As the option to turn off Custom Transaction Numbers is currently unavailable, you can set a notification to alert you when a duplicate invoice number is used.
Here's how:
- Click the Edit menu, then Preferences.
- Select Sales & Customers and go to the Company Preferences tab.
- Tick the Warn about duplicate invoice numbers checkbox.
- Choose OK to implement the changes.

Currently, if a sales receipt is saved with the number field left blank, QuickBooks won’t generate numbers automatically moving forward, and there’s no setting to warn for duplicates. To help keep things accurate, you’ll need to manually enter a unique number for each receipt. We know this isn’t ideal and appreciate your patience as we work to improve the process.
To help your customers keep track of their remaining balances and payments, check out this helpful guide: Create and send customer statements in QuickBooks Desktop.
Write down any additional questions in this forum, whether about transaction numbers or when navigating the different areas of QuickBooks Desktop. We always look forward to helping you with future concerns.