How to do alipay in ionic 4

I am new in ionic 4. I want to add alipay plugin in my ionic apps. I saw all the tutorial do like this only :

import { Alipay } from '@ionic-native/alipay/ngx';

constructor(private alipay: Alipay) {

//alipayOrder is a string that has been generated and signed by the server side.
   .then(result => {
      console.log(result); // Success
   .catch(error => {
      console.log(error); // Failed


But this only show the loading say openning the alipay but do not open the alipay page to pay. What I need to change inside the code? I want to send the total payment to use the alipay do payment. Anyone can help me?