If you get this error when paring your HomeKit device, please do as follows:

a. Check whether the smart accessory lost power supply by chance. 

b. Reboot your iOS so that the Home app will clear its cache. And then retry.

c. Power cycle the accessory. For light switch, please reboot it at the circuit breaker.

d. Login to your Wi-Fi router to see whether it is running any MAC filtering or Access Control function. If yes, please turn it off until the accessory is successfully added.

If you still have issue, please contact Meross Support.