The synchronization of the NEKDASH web service is not working correctly

How to properly chain HTTP calls; I have an issue with the NEKDASH webservice.

vue-general.ts

export class VueGeneralComponent implements OnInit {
  private unsubscribe$ = new Subject<void>();

  vueGenerale: {
    preaPerimes: Number;
    preaNonTraiter: Number;
    clientDebiteurTit: Number;
  }


  constructor(private service: VueGeneralService, private router : Router) {
    this.vueGenerale = {
      preaPerimes : -1,
      preaNonTraiter : -1,
      clientDebiteurTit : -1
    }
   }

  ngOnInit(): void {
    this.getVueGeneral();
  }

  ngOnDestroy(): void {
    this.unsubscribe$.next();
    this.unsubscribe$.complete();
  }


  getVueGeneral(): void {
    this.service.getVueGeneral().pipe(
      takeUntil(this.unsubscribe$)
    ).subscribe(res => {
      this.vueGenerale.preaNonTraiter = res.PREANONTRAITER;
      this.vueGenerale.preaPerimes = res.PREAVISPERIME;
      this.vueGenerale.clientDebiteurTit = res.CLIENTDEBITIT;
    })
  }
  
  getClass(value) {
    if (value == 0) {
      return 'green-alert-card';
    } else if (value > 0) {
      return 'red-alert-card';
    } else {
      return 'gray-alert-card';
    }
  }

  goTo(dest: string) {
    this.router.navigateByUrl(`/dashboard/${dest}`);
  }
}

vue-general.service.ts

@Injectable()

export class VueGeneralService {
  private readonly api: string = environment.api;

  constructor(private http: HttpClient, private store: Store) { }



  getPreavisPerime(): Observable<PreavisResponse> {
    return this.http.post<PreavisResponse>(this.api + `/NEKPREP`,{
      FILTRE:{
        STATUT: 2,
        MODE : 'PREAP',
      }

    }, {});
  }

  getPreavisNonTraiter(): Observable<PreavisResponse> {
    return this.http.post<PreavisResponse>(this.api + `/NEKPREP`,{
      FILTRE:{
        STATUT: 1,
      }

    }, {});
  }

  getPreavisNonTraiterListe(client: string): Observable<PreavisATraiterResponse> {
    return this.http.post<PreavisATraiterResponse>(this.api + `/NEKPREL`,{
      CUSTOMER:{
        REFERENCE : client
      },
      FILTRE:{
        STATUT: 1,
        MODE: ""
      }

    }, {});
  }

  getClientsDebiteursTitres(): Observable<ClientDebiteurTitre> {
    return this.http.post<ClientDebiteurTitre>(this.api + `/NEKCLDT`,{
      PAGEIN: {
        NTH: 1,
        SIZE: 999
  }

    }, );
  }

  getVueGeneral(): Observable<VueGenerResponse> {
    return this.http.post<VueGenerResponse>(this.api + `/NEKDASH`,{});
  }
}

Thank you in advance for your help.