t long last, you don't have to void an invoice and start over again if there are item(s) that should not have been on that invoice!!
Here is the concept of how it works.  If you need to remove a line item (activity) from an invoice that you have created, you can do so by going to the Request/Job that contains the activity and clicking the remove button on the activity you need to "uninvoice".  see below that invoice #194 has two items.  One for Req# 1415 and another for Req# 1416.  Let's say we should not have invoiced #1416 yet, but we did, accidentally.

Find the job on the Dashboard and go to the Actuals Tab and scroll all the way to the right.  See the Remove button in the last column.

Click that button and click 'Yes' to confirm your intentions.

When you click yes, the Invoice # and Invoice date will be removed.

Go back and reprint the invoice and that item will no longer be there.

One thing you have to remember if you use Quickbooks is that this process does not transfer the fix to Quickbooks.  You will have to do that manually.