1. The user's own mobile phone number is blocked by the operator; 2. Blacklist settings such as SMS security software; 3. Privacy settings of the built-in browser of the mobile phone; 4. The number of short messages sent by users exceeds the maximum limit of one day; 5. Network wireless network and communication delay.

The mobile phone verification code is a verification code set by related websites to verify identity, because a mobile phone number can only be held by one person, not by several people, which provides convenience for mobile phone to verify personal identity. As long as the mobile phone is in a person's hand and held for a long time, it means that the mobile phone number belongs to that person. By sending the verification number, you can verify whether he is online or stolen.