angular6 - I can't get response from Scopus API - httpresponse

Question

I want to use the Scopus API to verify that a DOI exists. I'm using the "Cited By" option. I did a test of this "http://api.elsevier.com/content/search/scopus?query=DOI(10.1016/j.stem.2011.10.002)" link in POSTMAN and it works, but when I did the implementation in Angular this is what returns.
Angular code
let headers = new Headers({
'X-ELS-APIKey': apikey,
'Accept': 'application/json',
});
this._http.get('http://api.elsevier.com/content/search/scopus?query=DOI(' + doi + ')', { headers: headers }).pipe(map(res => res.json())).subscribe(
response => {
console.log("Response");
console.log(response);
},
error => {
console.log("Error");
console.log(error);
}
);
Any help is greatly appreciated :)

Answer 1

Finally I solved it, the problem was that the "doi" string needed to go through the encodeURIComponent() function. I leave the code in case someone needs it.
welcome.component.ts:
let doi = encodeURIComponent('10.1017/j.stem.2011.10.002');
this._scopusService.getPublication(doi).subscribe(
response => {
console.log("DOI exists");
},
error => {
console.log("DOI doesn't exists");
}
scopus.service.ts:
public getPublication(doi) {
let headers = new Headers({
'Accept': 'application/json',
'X-ELS-APIKey': this.apiKey
});
return this._http.get('https://api.elsevier.com/content/search/scopus?query=DOI(' + doi + ')', { headers: headers }).pipe(map(res => res.json()));
}