Per the issue, pls kindly check below steps:
1. Please make sure the router you are using is properly connected to the external network, synchronize and power off and restart the router, if the router comes with HomeShield Pro function, please turn off the HomeShield Pro function or authorize to let X1 access, this function may prevent the HUB access.
2. Because the HUB only supports WIFI 2.4GHZ, please make sure that the HUB is directly connected to the router, and try not to pass the Mesh Router in the middle. If there is a Mesh Repeter, it needs to be set to WIFI2.4G
3. Make sure that the mobile phone and the HUB are connected to the same router, the mobile phone must also be connected to the same router to discover the HUB device in the local area network.
FYI, Make sure that the distance between the HUB and the router is not too far.
4. If still no help through the above actions, please share a hotspot with another mobile phone, use this hotspot as a router, connect both the HUB and the mobile phone to this hotspot, and then see if the hub can be added or not,