You may be getting the pairing error while trying to pair the app with the Air Purifier because of any one or more of the following issues - 

1. Please check if the Wi-Fi Router password entered is correct.
2. Bring your Air Purifier and the mobile device (app) closer to your WiFi Router less than a meter apart (less than 3 feet).
3. Make sure you are using 2.4 GHz Wi-Fi SSID as this Air Purifier does not support 5 GHz Wi-Fi.
4. If you use a Mesh Router, you may need to re-try as Mesh Router may switch between 2.4GHz & 5GHz periodically.

5. Retry Pairing Process.