Problem
You need to charge or remove tax but the invoice was already exported so you're unable to include or remove the tax to the total.
Solution
Search for the invoice for which you want to add or remove tax.
In the invoice screen, select Add an adjustment invoice.
In the adjustment invoice screen, select Add a task.
In the Add a Task screen, add the same task from the original invoice but in negative quantity. For example, if the original task has a quantity of 1, enter "-1."
When finished, click Save. The balance on the original invoice should be clear.
In the invoice screen, select Add an adjustment invoice to create a second adjustment invoice.
In the new adjustment invoice, add the same task from the original invoice.
Depending on whether you want to add or remove tax:
Select the Taxable option if you want to add tax.
Clear the Taxable option if you want to remove tax.
Note: Account configuration may be required. If you do not see the Taxable option, contact Technical Support to enable this feature.
When finished, click Save.
Check the total in the adjustment invoice to make sure the total includes the tax.
When finished, click Save.
Check the total amount to make sure the tax is included.