The opt-out option is an operation where a user requests to stop sending him or her advertising materials and messages to mobile phones or chat application.
The opt-out function mostly is used by marketing departments to give the opportunity to unsubscribe from the advertisements he receives.
The use of opt-out varies worldwide and in some countries the opt-out function is an obligatory part of message text by law. The opt-out or directions on how to opt-out is usually placed at the end of a message.
Apps for chat like Viber have an opt-out option for A2P messages at the top of the chat group.