Hiya Kris! Thanks for joining the Community Forum.
There are two good options for you here. The first would be to raise the invoice for the actual amount received, instead of the total including the vehicle hire.
Alternatively, if you want to display the deduction, you can do this using the ‘Discount’ button within the line item section. Put “Vehicle Hire Deduction” in the description (or something similar) and enter the amount of the cost. A heads up - it will say “Discount” on the line item - this can’t be changed, currently.
If further info is required about the hire, you can use the ‘Sales Invoice Note’ section to add more detail.
Hope this is helpful!