The most probable case is you temporarily exhausted the Video Ad inventory. Oftentimes, despite the fact that the button is available, videos may not play after tapping on it. This also means there aren’t any ads available. Unfortunately, the availability of those videos depends on the ad network’s inventory for each geographic region and device.
The button to watch videos disappears when there aren’t videos available to be played. If the button to watch more videos button is inactive that’s most probably because you’ve run out of inventory of videos to watch for now. We suggest you come back to watch more ads the next day (at least 24 hours) for videos to stock again and see if you can run more videos. Please try this and us know if this works. Alternatively, until Video Ads are stocked again, you can refill fuel by inviting friends, or waiting for fuel to normally refill with time.