Hello stewart3,
There is currently no feature for a line by line discount. The workaround would be to create a duplicate product, with a discounted rate, and mention that this is the discounted product in the name. Then, when setting up the invoice, you can select this product and it will show as 'discounted' on the customer's side.
Please use the cog wheel within your account to leave feedback - your suggestion will be submitted directly to the developers who will look into implementing this in future updates, if possible.
Thanks,
Talia
