How does generative credits work?

Can anyone tell me how generative credits work? I've been a subscriber to Adobe for many years and now Adobe has come up with new tools that I'd like to use. It's about Firefly Video. It says it costs generative credits to use it, and you're constantly told how to buy them. I already have generative credits, but apparently I'm not allowed to use them to make videos. So I can understand there are two types of generative credits that can be used for different things, even though you call them the same. It's pretty confusing and right now I don't understand. It looks like Adobe wants me to create a whole new subscription, next to the subscription I already have, to even be allowed to use firefly video. Why does Adobe choose to introduce two different generative credits that can be used for different things, but at the same time choose to call them the same?

- Unfortunately, there is no option to choose a topic that really fits this post - unfortunately, that's how it is every time. So the only thing I could choose was "Audio and Video".