Build a referral program

I need a simple referral program built using any kind of existing online referral software tool. Step 1. Set up a webpage where people can register for the program [We can do this] Step 2. They get a code by email that they give to their contacts/clients. This gives the client/contact $5 discount when they buy a specific product. Step 3. The referral partner gets $5 for every payment. We use Squarespace for our website. But I don't mind if it sits on a separate platform. If we can get the first one working then we will have a second one to do.