If your invoice is in an editable status (N, IP, R, RE), and you are the owner of the invoice, you can remove extra coding lines for an invoice in the details view by:
 
Selecting the rows you want to delete by clicking on the row, or if you want to delete more than one row, hold down the 'Ctrl' key on your keyboard while you 'Left Click' with your mouse to select multiple rows (all selected rows will be highlighted in blue). Once they are selected, click the 'Edit' button at the top right corner of your line items panel.

A menu will pop up, choose the 'Delete' option.

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