This error typically happens if you undo invoices back to drafts and submit other invoices in the meantime. Quickbooks will retain the "used" invoice number in their system so when you attempt to resubmit the invoice, it will flag an error.
It can also be the result of someone setting a number manually on a draft invoice or an invoice in QuickBooks and causing the sequence to pick up from there.
Fix 1: Set a new number on the draft
The way to fix it is to set the draft to a number higher than what you have in QuickBooks already.
Note: Make sure it's higher than the highest invoice number in QuickBooks so you don't run into the issue again!
You can set the new number here on the draft invoice:
How to find the next available invoice number
Navigate to the "Manage Invoices" area within LeanLaw.
Ensure that any existing filters are cleared to display ALL invoices.
Click on the "NUMBER" column header to sort the invoices in descending order (highest number first).
The highest invoice number displayed at the top of the list is the most recently processed number. The next invoice created should be one number higher.
Fix 2: Turn off custom transaction numbers
NOTE: Turning off Custom Transaction Numbers in Quickbooks will allow multiple invoices to share the same invoice number. Only use this option if it fits your business needs.
Here are the steps in QuickBooks Online:
Click the gear ⚙ icon in upper right corner
Click "Account Settings" in the upper left column
Click "Sales" in left column
Click into "Sales form content"
Turn off "Custom transaction numbers."
Click "Save"
Click "Done"
If you have any further issues, please reach out to our
Customer Success and Support team!