Hello, I've installed the Tello apps on my smartphone and connected it to the Tello Edu aircraft and used it well.

By the way, the apps does not work because I try to connect to another Tello Edu aircraft.

To describe the exact state,
1. Video captured on the camera of the Tello Edu aircraft appears on the apps screen.
2. All buttons of the apps do not work.
3. A message "Warning: Not Activated" appears at the bottom of the screen.

What's the problem?
For reference, the battery is over 90%.