Getting error "uncaught app1: application 'app1i' died in status LOADING_SOURCE_CODE: "does not export an unmount function or array of functions" in signle-spa

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Angular8

I am implementing single-spa(for micro front end) in existing project which is in angular 8. Installed single-spa in app1 using command "ng add single-spa-angular" and in root app I am importing and registering this app, but getting error like "

Uncaught app1: Application 'app1' died in status LOADING_SOURCE_CODE: "does not export an unmount function or array of functions

" searched it error on google but still not able to resolve. Please help

What I have tried:

//index.html in root app which is not angular
<pre> <script type="systemjs-importmap">  
  {
        "imports": {          
          "app1": "http://localhost:4200/main.js",              
          "single-spa": "https://cdnjs.cloudflare.com/ajax/libs/single-spa/4.3.5/system/single-spa.min.js"
        }  
  }

<script>
    System.import('single-spa').then(function (singleSpa) {
 singleSpa.registerApplication(
          'app1',
          function () {
            return System.import('app1');
          },
          function (location) {
            return true;
          }
        );   
 singleSpa.start();
      })

In angular.json using builder as:

"architect": {
        "build": {
          "builder": "@angular-builders/custom-webpack:browser",
}
}

in package.json done changes like

"start": "concurrently \"npm run start:server\" \"npm run serve:single-spa\"",