What does mx5 short message group mean that the recipient is invalid?

I guess you haven't added the recipient yet, and then click the send button. Otherwise, the phone number you entered is wrong. You can check it from Xinfa. There are certain restrictions on texting on mobile phones. If the number of SMS messages exceeds 200 per hour, this function will be turned off. If more messages are sent, it is recommended to send them on onesmser SMS platform.