I need one = You pay $20.00 and gets the template to use in your artwork. No need to include a white space holder for it since it is an overlay.
I have one = You already have a code and it is embedded in your artwork. We'll ask you to type in your code as a “verification” that the code is valid.
I don’t need/want one = Not doing any type of physical sales that you will be tracking nor is there a code embedded in your artwork.