If you are attempting to create a member for a specified group with a private sensor, sensor_id will not work (the six-digit key associated with the sensor). I have only had this API call work with the MAC address (12 character address with colon format included).
Hi @Alana_V, I have just tried this myself and was able to add a sensor using its sensor index. Can you share the request you are making?
Please note that the “sensor_id” is the 12 character MAC address, and the “sensor_index” is the unique 4-6 digit code.