The Custom Transaction Number setting in QuickBooks lets you manually assign invoice numbers. We recommend turning off this setting to prevent QuickBooks from attempting to reuse invoice numbers. This guide walks through how to turn off this setting.
How to Turn Off This Setting
Log in to your QuickBooks account and go to Settings ⚙, then select Account and Settings.
Select Sales
In Sales Form Content, select Edit ✎.
Turn Custom transaction numbers off.
Select Save, then select Done.
If this setting is left on:
If this setting is left on, QuickBooks will eventually try to reuse invoice numbers. When you try to invoice jobs on the Invoicing and Job Records, you will run into the error below:
“QuickBooks: Validation Exception was thrown.Details: Duplicate Document Number Error: You must specify a different number. This number has already been used”
Disabling the Custom Transaction Numbers setting will fix this error. You will need to disable this setting, then try invoicing jobs again.
My Invoice Numbers Are Wrong or Have Strange Characters/Letters:
Occasionally, you may find that your invoice numbers may not look correct or normal. This can happen if an invoice number was changed manually in QuickBooks. This is where you can enable Custom Transaction Numbers.
To correct invoice numbers
Log in to your QuickBooks account and go to Settings ⚙, then select Account and Settings.
Select Sales
In Sales Form Content, select Edit ✎.
Make sure Custom Transaction Numbers is on.
Select Save, then select Done.
Do not create any new invoices while this setting is on.
Go into the invoice(s) and correct the invoice numbers if needed.
Once you are done correcting invoice numbers, you need to turn off the Custom Transaction Numbers setting.
If you do not need to correct invoice numbers, you can turn off the Custom Transaction Numbers setting and invoice jobs like normal. This should reset the sequence.
If you are still having issues with invoice numbers after taking these steps, you will need to contact QuickBooks support for additional help.