Solution:
Method 1. Enter Mi TV and box setting - Account and Security - Login Mi account (this account shall ensure the same account for Mi TV and box and Mi Home APP on mobile phone)
Method 2. The mobile phone and Mi TV and box are connected to the same LAN, open the Mi Home APP- my device - click the "login" button on the right side of Mi TV and box in the current LAN, and enter the Mi account password to bind.
Notes:
After successful binding, use Mi Home APP to remotely control Mi TV and box, and ensure the phone is connected to the same LAN with Mi TV and box.