Angular 4 http request every second

Question

I am trying to call my API every second. I don't know how to do.

For call on time is ok :

loadRequest(payload: any): Observable<RequestTask[]> {
    const headers = new Headers({'Authorization': localStorage.getItem('authorizationToken')});
    const options = new RequestOptions({headers: headers});
    const requestId = payload;
    const url = '/api/requests/'+ requestId +'/events'

    return this.http
        .get(url, options)
        .map(response => {
            const requests = response.json();
            console.log("Request API", requests)
            return requests.map(request => {
                return new RequestTask(request)
            });
        })
        .catch(this.handleError);
}

My test for call every second

loadRequest(payload: any): Observable<RequestTask[]> {
    const headers = new Headers({'Authorization': localStorage.getItem('authorizationToken')});
    const options = new RequestOptions({headers: headers});
    const requestId = payload;
    const url = '/api/requests/'+ requestId +'/events'

    return Observable.interval(500)
        .flatMap(()=> {
            return this.http
                .get(url, options)
                .map(response => {
                    const request = response.json();
                    return request.map(request => {
                        return new RequestTask(request)
                    });
                }).catch(this.handleError);
        })

}

I think my error come from Observable but I don't see how solve it