What type of plan are you on, enterprise or personal?
If you are on an enterprise plan, your enterprise plan has to have Firefly Video on the plan. Please contact your local Adobe administrator. If Firefly video is not on your enterprise plan, they can contact your organisation's Adobe account representative to enquire about adding it. [Note, if you are on a school or university enterprise plan, Firefly video is not currently available on those plans.]
If you are on a personal plan, Adobe Firefly video is a premium service which requires a separate Firefly premium plan. For more information, please see the pinned reply in this post: P: Plan error in generating video.
Note that all accounts received two complimentary Firefly video generations. After those were consumed, you have to be on a plan that includes Firefly premium features.
If you have purchased a premium Firefly subscription or you have access to Firefly premium services on an enterprise plan, please include a screen shot of the whole browser window (including you avatar in the upper right corner) with the error showing, and then please click on your avatar in the upper right corner and take a screen shot of that box, blacking out your personal details. Please also tell us your operating system and browser along with the version numbers.