1. Click new invoice.
Make sure to select one invoice.
If you already have an invoice created that you like to add Flat fees to, navigate to that invoice and click on edit.
2. Click Add line.
This will create a new line to your Flat Fees and will allow you to enter custom items in each line.
3. Fill out all the columns.
If you have a smaller screen, use the scroll bars to see the rest of the columns. Make sure to save your changes.