Find your product ID
To find or edit the product ID for implementing the Gumroad Overlay on your site, simply go to your Products dashboard and click the name of your product.
In your browser's address bar, you'll see the following: "gumroad.com/products/XXXXX/edit", where your product ID is the five letters in the "XXXXX" space of the address.
Next to the Publish and Save changes buttons is a box with your product's URL. Click in this box to change your product ID and create a custom URL.