If the user has requested a confirmation code by phone number, but the SMS with the code does not come, the reasons for the error may be:
- inactive phone number (non-existent is specified),
- negative balance (for some operators),
- the number is blocked by the operator,
- the subscriber has disabled the delivery of messages on the guaranteed channel,
- device memory is full.
- in addition, the operator insures subscribers from spam and if a message with the same text is sent to the number many times within 1 minute, then only one message comes, all the others fall into error.
The confirmation code is sent to the phone after the waiting time has passed, the code is no longer accepted.
There are many factors regarding the speed of sending. This may be both poor communication regarding the reception of messages, and moderation on the part of the operator.