The cause is one of the followings. 

1

The registered devices might be over the limit.
Up to 10 remote controls/smartphones can be registered to 1 door in total. 

 2

The door is either closed or locked. 
Please open and unlock the door before registering remote control. 

 3

The remote control's power might be OFF. 
Please press both buttons of the remote control for a certain duration to turn ON the power.

 

4

There might be an abnormality in door's power source. 

【When using batteries】
Please reinsert batteries in correct manner or change the batteries.
How to change batteries

【When using AC adapter】
Please make sure that the AC adapter is connected with the power outlet.

【When using controller unit】
Please make sure that controller unit's power is turned ON.