The cause is one of the followings. 

1

The door might be closed or locked when registering.

Please open and unlock the door before registering.

 

 2

Inside lock button power might be turned OFF.
Please press both buttons at the same time and maintain the motion for a certain duration to turn the power back ON. 

 3

The transmission might be interrupted by the signal of same type which results in connection problem for inside lock button.
Please check the followings.
・Are there multiple electronic devices of 2.4 GHz frequency in in the area ?
・Does the 2.4 GHz WiFi router have more than 2ch ? 
※It is highly likely that the transmission will be interrupted by the signal emitted from 2.4 GHz WiFi router with more than 2ch. 
Please change the router setting to 5GHz if possible.
 

4

The transmission distance exceeds 3 meters. 
Please use/register the inside lock button within 3 meters distance from the door. 

 5

The transmission will become weaker when there are obstacles such as metallic objects, RC walls, human bodies, beverage, electronic devices blocking between the inside lock button and the door. 
Please avoid the above-mentioned objects when installing/registering. 

6

Version of door control program might not support the inside lock button.
Please check from My Entrance application whether if door control program version is more than 「ver2.1」.
How to check the door control program

 7

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.