Angular 6 HttpClient API Requests Not Being Made

Question

I have an ApiService in Angular 6 with the following function:

 add(data, string: string, type): Observable<Object | Response> {
    return this._http.post(this.url + string, data).pipe(
      tap(() => this.log(`added ${type} successfully`)),
      catchError(this.handleError<Response>(`Adding ${type}`))
    );
 }

This function is called in a component as follows:

this.api.add(this.parent, 'parents/new', 'Parent').subscribe(() => {
 this.authService.login(this.user, 'login').subscribe();
 this.router.navigate(['/register/student']);
});

The calls to the api are not firing at all even though I've subscribed to the Observable. Please help me out guys. Thank you