Launch the app and ensure you are logged into the Xiaomi account that owns the router. On the main dashboard, you should see your Mi Router AX1800 card. Tap on it to enter the router management screen.
Symptom: You enabled both 2.4 and 5 GHz, but your guest phone only sees one.
Fix: Some client devices cannot see 5 GHz networks if they are on a DFS channel (radar avoidance). In the web panel, go to Wi-Fi Settings -> Guest -> 5 GHz band and manually change the channel to 36 or 40 (non-DFS). Save and reboot. create guest network on xiaomi mi router ax1800 work
The preferred method for most users.