Error: advanced-http value must be string Ionic - api

Question

I have try to user #angular/http to send my api but I got the 401 polyfills error so I change it to #ionic-native/http , but then I got yet another error which is :Error: advanced-http value must be string" so I log my header and it was empty???
The log
"normalizedNames": {},
"lazyUpdate": [
{
"name": "Authorization",
"value": "Basic xxxxxxxx",
"op": "a"
},
{
"name": "Content-Type",
"value": "application/x-www-form-urlencoded",
"op": "a"
}
],
"headers": {},
"lazyInit": {
"normalizedNames": {},
"lazyUpdate": null,
"headers": {}
}
mycode
import { HTTP } from '#ionic-native/http';
constructor(public http: HTTP) {}
login(username, password) {
let body = {
username: username,
password: password
};
let headers = new HttpHeaders();
headers = headers.append('Authorization', 'Basic xxxxxx');
headers = headers.append('Content-Type', 'application/x-www-form-urlencoded');
return this.http.post(apiUrl, body, { headers: headers })
.then(data => {
console.log(data.status);
console.log(data.data); // data received by server
console.log(data.headers);
})
.catch(error => {
console.log(error); // error message as string
});

Answer 1

try this.
add this to your app.module
import { HttpClientModule } from '#angular/common/http';
imports: [
BrowserModule,
HttpClientModule,
IonicModule.forRoot(MyApp)
],
then in your code
//import { HTTP } from '#ionic-native/http';
import { HttpClient } from '#angular/common/http';
constructor(public http: HttpClient) {}
login(username, password) {
let body = {
username: username,
password: password
};
let headers = new HttpHeaders();
headers = headers.append('Authorization', 'Basic xxxxxx');
headers = headers.append('Content-Type', 'application/x-www-form-urlencoded');
return this.http.post(apiUrl, body, { headers: headers })
.subscribe(data => {
console.log(data.status);
console.log(data.data); // data received by server
console.log(data.headers);
})
.catch(error => {
console.log(error); // error message as string
});

Answer 2

thread quite old but might be can help others. Change your headers like below and test.
return this.http.post(apiUrl, body, { headers: 'Content-Type: application/json', Authorization: 'Basic xxx'})....