bookingpress_modify_email_notification_content

    add_filter('bookingpress_modify_email_notification_content', 'bookingpress_modify_email_notification_content_func', 10, 4);
    function bookingpress_modify_email_notification_content_func($bookingpress_notification_message, $bookingpress_appointment_data,$notification_name,$template_type)
    {
        // Modify the subject and/or content of the email notification!
        // Use placeholders in the subject and/or content to modify them
        // for example, you can place the %my_custom_placeholder% in your subject/content of the email notification
        // then you can replace it as following

        $bookingpress_notification_message = str_replace( '%my_custom_placeholder%', 'my custom placeholder content', $bookingpress_notification_message );
      
        return $bookingpress_notification_message;
    }