How to use Xiaomi's network short message? I can't find it.

Xiaomi mobile phone must send SMS: 1, and both parties use MIUI with SMS function; 2. Both parties have enabled SMS; 3. Both parties are connected to Wifi or data mobile network; Operation mode: 1). You can send network short messages like ordinary short messages. Enter the other party's mobile phone number in the recipient field, click on the content input box and wait for a few seconds. If network messages are available, the border of the content input box will turn blue. If the network short message is not available at this time, the border of the input box is green; 2) After the message is sent, if it is a short message, the background will be blue, otherwise it will be green; 3) The background of received messages, whether online or ordinary, is white.