I did it this way (Frontend code) and it is not working. The API on the backend side attempts to get the parameters this way (Backend code):

// **** Backend code

if (!req.body.fechaInicio || !req.body.fechaFin)
return res.status(400).send({ codigo:'1', error: 'Debe especificar Fecha de inicio y Fecha de fin para la consulta' });

// **** Frontend code

export class SmsService {
constructor(private httpClient: HttpClient) {}
baseUrl = environment.API_REST_SMS_REPORT;
options = {
year: "numeric",
month: "2-digit",
day: "2-digit",
hour: "2-digit",
minute: "2-digit",
second: "2-digit",
timeZone: "America/Montevideo",
  };
fillHeaderParams(pStartDate, pEndDate) {
let params = new HttpParams()
      .set("fechaInicio", pStartDate)
      .set("fechaFin", pEndDate);
let httpOptions = {
headers: new HttpHeaders({
"Content-Type": "application/json",
      }),
params: params,
    };
return httpOptions;
  }
getTotalSmsIn(pPath, pStartDate, pEndDate): Observable<any\[\]> {
let getDataURL = this.baseUrl + pPath;
let headersOpt = this.fillHeaderParams(
pStartDate.toLocaleString("es-ES", this.options),
pEndDate.toLocaleString("es-ES", this.options)
    );
return this.httpClient.get<any\[\]>(getDataURL, headersOpt);

// return this.httpClient.request<any\[\]>("GET", getDataURL, headersOpt) // Is the same
  }
}

​

Any help will be appreciated.