MESSAGE

"Duplicate Document Number Error : You must specify a different number. This number has already been used."

RESOLUTION

The message appears because a transaction already exists in QuickBooks Online with this number. 

In order to allow QuickBooks Online to use duplicate numbers, the following changes need to be made in QuickBooks Online:

• For Sales Transactions: Click the Gear Icon in the upper right-hand corner and select Company Settings. On the Sales tab in the Sales Form Content section, turn off Custom Transaction Numbers.

• For Bill and Check Transactions: Click on the Gear Icon in the upper right-hand corner and select Company Settings. On the Advanced tab in the Miscellaneous section, turn off Warn if Duplicate Check Number is Used and/or Warn if Duplicate Bill Number is Used.