Diagnosis
This is a known, finicky process with the M2. The hub needs to be on the same network *segment* as your iOS device, and Apple's HomeKit protocol is very strict about this during accessory pairing.
How to Fix It
First, ensure the hub is fully set up and working in the Aqara app, with a solid white light. In the Aqara app, go to the hub's settings and tap "Add to HomeKit." When the camera view opens to scan the HomeKit code, use the code printed on the *bottom of the physical hub*, not a screenshot or the code in the app. Make sure your iPhone/iPad isn't using a VPN or cellular data; it must be on the same 2.4GHz Wi-Fi as the hub. The process often fails silently—if it doesn't work after a minute, force-close the Home app and the Aqara app and try again from the start.
If That Didn't Work
Your network setup might be the issue. If you have a router that creates separate 2.4GHz and 5GHz networks with different SSIDs (names), ensure your phone is on the 2.4GHz one. More complex setups with VLANs or multiple access points can also block the mDNS/Bonjour traffic needed for HomeKit discovery.
Heads Up
Once added to HomeKit, the hub will appear as a "Bridge." Do *not* remove this bridge from the Home app unless you want to reset and re-add all your Aqara child devices to HomeKit again. It's a huge pain.