You can create discount item

as in, just a discount item, not linked to a promotion record?

Hmm you should be able to create the codes , I don’t have an account that I can test it

I could create single-use codes and not give them to customers, but I'm looking for a single code that our employees can use multiple times on warranty orders 😕 It doesn't look like there's an option for that though.

There is a way to create one code that you can use multiple times but it won’t be single use code because as name suggests single use are meant for one time use or one time use per customer

Right, I'm aware of that (shouldn't have called it a single code since that sounds too close to single-use code). I think what I'm looking for doesn't exist though. I want a multi-use code that can't be used by any customers on our websites but can apply to all customers when added by an employee.

you can create the code and make it complicated so not easy for people to guess and give them to your employee so it can be used internally but not on the website.

you could create the code, have it set to a zero amount. that way if someone tries it online, it wouldn't have any effect. Then instruct your users on how to change the values (or override) to do what you want.