private appointmentEndPoint$ = this.configurationService.fetch(
    config => config.appointmentsEndpoint
  );
  private serverUrl = this.configurationService.fetch(config => config.serverUrl);

  public getAppointments(patientIdentifier: string | undefined): Observable<any[] | undefined> {
    return combineLatest(
      [
        this.serverUrl,
        this.appointmentEndPoint$,
        this.serviceActivator
      ]
    ).pipe(
      switchMap(([serverUrl, endpointPath, _]) => this.http.get<any[]>(serverUrl + endpointPath + '/' + patientIdentifier)),
      catchError(error => {
        this.errorService.postError(error);
        this.napSDK.sendMessage(this.createNapErrorMessage(error)); // indicate to the host that something went wrong
        return of(undefined);
      }),
    );
  }