Thanks for your reply. Firefly video is considered a premium Firefly service and is not available on creative cloud plans. It requires a Firefly premium plan. Text to image and generative fill are not premium services and are available on creative cloud plans. I explain this in more detail in the pinned message in this thread: P: Plan error in generating video
What I can't understand is why Adobe don't explain it clearly to me instead of putting a text with a childish drawing that says "there has been an error" making me waste so much time.
I am sorry for that. There is supposed to be a popup window that prompts you to subscribe to a premium Firefly plan. I am not sure why you are not seeing that. I have submitted that issue for a further look.