Ionic 4 Http failure response for (unknown url): 0 Unknown Error. when calling api on real device

I have an ionic 4 application which calls a .NET Core backend api. It works correctly on chrome browser, but when I run apk on android device, the response is:

{"headers":{"normalizedNames":{},"lazyUpdate":null,"headers":{}},"status":0,"statusText":"Unknown Error","url":null,"ok":false,"name":"HttpErrorResponse","message":"Http failure response for (unknown url): 0 Unknown Error","error":{"isTrusted":true}}

regarding to header I appended these options:

const httpOptions = {
    headers: new HttpHeaders({
        "Content-Type": "application/x-www-form-urlencoded; charset=utf-8" , 
        "Access-Control-Allow-Origin": "*", 
        "Access-Control-Allow-Headers": "Origin, Content-Type, X-Auth-Token, Accept, Authorization, X-Request-With",
        "Access-Control-Allow-Credentials" : "true",
        "Access-Control-Allow-Methods" : "GET, POST, DELETE, PUT, OPTIONS, TRACE, PATCH, CONNECT"  
       }) 
};  

I have already installed plugin: cordova-plugin-ionic-webview

and using HttpClient from "@angular/common/http"

My API hosted remotely, no ssl certificate used !

I googled all solutions, but none of them solve my problem

Finally, I could resolve problem after two days hardwork ! I migrated API calling from '@angular/common/http' to native http '@ionic-native/http/ngx' with this header:

        // create headers data
        const headers = {
          "Content-Type": "application/x-www-form-urlencoded; charset=utf-8", 
          'Accept': 'application/json, text/plain',
          "cache-control": "no-cache", 
          "Access-Control-Allow-Origin": "*", 
          "Access-Control-Allow-Headers": "Origin, Content-Type, X-Auth-Token, Accept, Authorization, X-Request-With, Access-Control-Request-Method, Access-Control-Request-Headers",
          "Access-Control-Allow-Credentials" : "true",
          "Access-Control-Allow-Methods" : "GET, POST, DELETE, PUT, OPTIONS, TRACE, PATCH, CONNECT",  
          };

The cons for me, For now on I have to test on a real device.