Currently Float only supports the classic one-time payment model on Gumroad. Create your product at https://gumroad.com/products and make sure to choose "Classic".
Gumroad allows you to set one price or a pay-what-you-want model. Both are supported on Float.
In the landing page editor, select the Gumroad product that you just created
Before you publish your Gumroad product, make sure you add your Float redirect URL to Gumroad. This URL should look like
By default, you should see this screen. Since we're redirecting buyers to the course, click "Redirect to a URL after purchase"
Set your Redirect URL (https://float.so/courses/<your-course>/course) and save your changes