To set up your discount codes, check out this article:
To apply a discount code that you've already set up, go to your Inspection Details page on your existing inspection. Scroll down to the "Internal" box.
Simply plug in the discount code you set up in your settings, and it will automatically apply to your fees when a customer inputs that code!
Customers cannot apply multiple discount codes to an inspection.
Here's how it will look to the customer: