Creates a SMS event subscription. A webhook_id is required so that we know to which url the events shall be sent. A SMS direction is also required in order to limit the direction for which SMS events are sent. Use 'all' to get SMS events for all directions. A target_type and target_id may optionally be provided to scope the events only to SMS to/from that target.
Note: To include the MESSAGE CONTENT in SMS events, your API key needs to have the
"message_content_export" OAuth scope.
Added on April 9th, 2021 for API v2.