bug: Http call only work on browser

Bug Report

Ionic version: [ ] 3.x [x] 4.x [x] 5.x

Current behavior: While running the application on mobile (debug mode), http calls return error as if they are not even called. Error: status: 0 Unknown error.

Expected behavior: Sending/Receiving data should take place, i have been calling the APIs from my browser and it worked just fine.

Related code:

    this.getPetTypesSub = this.myService.API_NAME(param).subscribe((data) => {
//doSomething
 }, (error) => {
      alert(JSON.stringify(error));
    });

  API_NAME(Param): Observable<any> {
   let url = 'API_URL/API_NAME';
    const headers = new HttpHeaders({ 'Content-Type': 'application/json' });
    const options = { headers: headers };
    return this.api.post(url , JSON.stringify(Param), options)
      .pipe(map(response => {  return response.; }));
  }

Other information: I tried to call an api that is working on another ionic application (Ionic 3). But calling it from (Ionic 4 - 5) application is not working especially on device.

Ionic info:

Ionic:

   Ionic CLI                     : 5.0.0 
   Ionic Framework               : @ionic/angular 4.4.2
   @angular-devkit/build-angular : 0.13.9
   @angular-devkit/schematics    : 7.3.9
   @angular/cli                  : 7.3.9
   @ionic/angular-toolkit        : 1.5.1

Cordova:

   Cordova CLI       : 9.0.0 (cordova-lib@9.0.1)
   Cordova Platforms : android 8.0.0
   Cordova Plugins   : cordova-plugin-ionic-keyboard 2.1.3, cordova-plugin-ionic-webview 4.0.1, (and 4 other plugins)

Utility:

   cordova-res : 0.3.0
   native-run  : not installed

System:

   NodeJS : v10.15.3
   npm    : 6.9.0
   OS     : Windows 10

[paulstelzer]

Thanks for your issue! Please aware that this Repo are only for Ionic issues. What you describe is more related to Angular and Cordova or Cordova Plugin Ionic Webview. What @KillerCodeMonkey says I also believe: the API server needs CORS enabled and set correctly.

[KillerCodeMonkey]

looks like more a config issue https://docs.microsoft.com/en-us/visualstudio/cross-platform/tools-for-cordova/security/whitelists?view=toolsforcordova-2017

maybe you are using a non ssl endpoint or something?