Are you getting an error? Were you able to generate more than two videos previously? Can you please include a screen shot of what is happening?
You might know this, but generating Firefly video is a premium service. If you are on a personal plan, after 2 free generations, you need to purchase a premium plan; either theFirefly Standard or Firefly Pro plan. If you are an enterprise customer, Firefly video is not included in all enterprise plans. You would need to speak to your local Adobe administrator about whether it is available to your organisation.