If you are new to using Gopher, you might have accidentally generated your invoices multiple times in your first month and not intended to do that. When you generate invoices it takes all of your jobs from your 'completed jobs tab' in your schedule page and creates invoices from them.
Usually you generate your invoices once a month at the end of the month. If you happened to generate invoices during the month and now have mulitple invoices for each customer and want only one invoice per customer you can do the following.
Taken from the post on 'ungenerating invoices' :
"If you are in your invoice section you can right click on the invoice and then left click in the pop up menu where it says ungenerate.
Ungenerate both invoices then go and generate your invoices again for that one customer and it will create one invoice."
Stop guess-timating. Learn how to estimate and make money! $$$