Why does the device lock not receive the verification code?

The reason why the device lock cannot receive the verification code:

The mobile phone system is malfunctioning; the bound phone number is incorrect; the bound mobile phone number has been changed; the use of mobile phone text messages is restricted ;The mobile phone number is in arrears. Solution:

Log out of the account and log in again; restart the phone and check for updated software; rebind the new mobile phone number; check whether the mobile phone number is in arrears.