When creating a transaction in QuickBooks, a transaction number will be generated followed by the last transaction created. In most of the applications, transaction number has to be unique and is not allowed to be modified to prevent duplication and confusion.
However, in QuickBooks, transaction number is allowed to be modified which means that when creating a new transaction, user can either use the transaction number that
is generated by the QuickBooks or modify this number to other value.
If the user attempts to create a transaction which the transaction number is same as the number of other transaction that has been created in QuickBooks,
a warning message will notify the user telling that a problem has occurred. User can still proceed with the modification.
There is another issue after modifying the transaction number, which is the transaction number counter will also be reset based on the last transaction number created.
For example, the original Invoice number generated is 1501, if a user changes this number to 101 and created this Invoice. The number for the next newly created Invoice will
If you want to integrate QuickBooks with another application, this issue should be taken into consideration because the transaction number may be used as an external ID
for the record. This external ID has to be unique to create a relationship between the record in QB and the other integrated application.