function send_message_to_student_113( $user_id, $tags_applied ) {

    $tag_id = wp_fusion()->user->get_tag_id( 'completed 1.1.3' );

    if ( in_array( $tag_id, $tags_applied ) ) {

        $args = array(
            'sender_id'  => 1,
            'thread_id'  => false,
            'recipients' => $user_id,
            'subject'    => 'Hello there',
            'content'    => 'You are getting this message because you completed the first lesson of this project',
            'date_sent'  => bp_core_current_time()
        );

        $result = messages_new_message( $args );

    }
}
add_action( 'wpf_tags_applied', 'send_message_to_student_113', 10, 2 );