1. Create your invoice by following this guide:
2. If the invoice is internal change the 'Internal Invoice' toggle on the right hand side to Yes.
3. Process the invoice on the bottom right of the screen.
4. The invoice is now marked as Internal. This can be useful when running your reporting. If you go to Reports > Business Reports > Sales Reports. There will be a range of Reports that have the field 'Internal Only'. When looking at these drop-down options you will be able to choose All, Internal Only or No Internal. This means that you can see choose to see any of these reports with reference to your external customers or your internal customers.