Angular 4: JSONP injected script did not invoke callback

I am new to Anguar4 and met this question:

JSONP injected script did not invoke callback

I tried different API for example: https://jsonplaceholder.typicode.com/posts

However, my api gives me this error. However, it works for jQuery, jsonp. I googled many resources online, spent many hours, but could n't fix it. Here is my code:

import { Injectable } from '@angular/core';
import { Http, Headers, Jsonp, URLSearchParams } from '@angular/http';
import 'rxjs/add/operator/map';

@Injectable()
export class ServerService{

    constructor(private jsonp: Jsonp){}

    getServers(term: string) {
                let url = `url`; 
                let params = new URLSearchParams();
                params.set('search', term); // the user's search value
                params.set('action', 'opensearch');
                params.set('format', 'json');
                params.set('callback', 'JSONP_CALLBACK');
                return this.jsonp
               .get(url, { search: params })
               .subscribe(
                (data) => {
                    console.log(data);
                },
                (error) => {
                    console.log(error);
                });
    }

}