Before the first time an aircraft takes off using the Ninja OBC system it will need to be registered with DJI. DJI controls what devices can take off on while talking to their aircraft. To do this, it must be plugged in properly and on the internet. This allows the aircraft to communicate with the Ninja, get it's App ID code, and send that to DJI for authorization.
This step will need to be done with all new installations of a Ninja or any time you move a Ninja to a new aircraft. If you purchase your hardware from Drones Made Easy this step will already be done.