How to add error message in a Suitelet page

let myMsg4 = message.create({
       title: 'ACKNOWLEDGEMENT STATUS',
       message: 'This Purchase Order is already Acknowledged',
       type: message.Type.ERROR
    });
    log.debug("myMsg4", myMsg4)
    myMsg4.show();
    form.addPageInitMessage({
      message: myMsg4
 });