If you have a sensor but is not working, it can be cause by different issues:
The ID of the sensor is wrong, please see here the instructions to change the ID of the sensor in the doors configuration.
The battery of the sensor has run out, please see here the instructions to change the batteries of the sensor.
The sensor needs to be less than 10 meters away from the ismartgate, in direct sight without any obstacles (like a brick wall or a metal door). Please try taking out the sensor and moving closer to the ismartgate. Can you see a status change in the app?
Move the sensor just like the door would.
The ismartgate's status light will blink faster each time it detects the sensor. In case this does not happen please send an email to firstname.lastname@example.org.
The sensor is not correctly placed, see the placement of the sensor depending on which type of door you have: