Hey there, PROSIX.
Welcome to the Apple Support Communities. We understand how important it is to be able to use your HomeKit accessories.
To start, make sure the accessory is set up according to these steps: Add a HomeKit accessory to the Home app
If the issue continues, ensure that you are using a compatible device (iOS 10 or later, tvOS 10 or later, macOS 10.14 or later or watchOS 03 or later). Ensure that Bluetooth and Wi-Fi are both enabled, and connected. Finally, unplug and plug in the accessory.
Should the issue continue, consider the following questions.
- Are iCloud Keychain and Home enabled in Settings > [your name] > iCloud?
- Does the manufacturer app have any updates?
- Have you checked the accessory manual to ensure that there are no extra hardware requirements?
All the best.