the price I set for the Key Group
What's a key group price?
Customers on Itch are people buying for their account. You do not buy keys in bulk, that you can redistribute. And bought projects are in the library of the customer. You cannot revoke the license to the project. Read the tos about this Publishers hereby grant ... to Users, a non-exclusive, perpetual license to access the content ... Users shall retain a license to this content even after the content is removed from the Service.
A pay per play business model is not viable on Itch. Itch is a classical pay per project store with some extras and some shortcomings. If you need drm, that will be a hassle to implement. But even if you do, the only thing you can verify, is if an account has purchased the project, and maybe how much was paid.
I think you might refer to this https://itch.io/docs/creators/download-keys#download-keys-and-urls/bulk-keys
If you generate a key, you can set a price that this key would unlock. Since you generate the key, it has no price. But Itch needs to know the unlock price, in case there are individually priced files. The key itself will unlock all regular files on that project. But you can have files that are locked, unless someone overpaid. As explained by hechelion.