Observable> is not assignable to type Observable httpclient angular

Question

i have a http get request in my angular app, it looks like :

 getAll():Observable<TransaksiDetail[]>{
    return this.http.get<TransaksiDetail[]>(`${BASE_API()}/transaksi`, this.httpOptions);
  }

then i run ng serve the app is running well but in cmd it's showing an error like:

webpack: Compiled successfully. ERROR in src/app/services/transaksi.service.ts(56,5): error TS2322: Type 'Observable>' is not assignable to type 'Observable'. Type 'HttpEvent' is not assignable to type 'TransaksiDetail[]'. Type 'HttpProgressEvent' is not assignable to type 'TransaksiDetail[]'. Property 'includes' is missing in type 'HttpProgressEvent'.

and i try to access the page who call getAll() method and it's running well too

this is my class :

export class TransaksiView {

  nama_pembeli:string;
  id_toko:number;
  nama_toko:number;
  jumlah_beli:number;
  total_harga:number;
  status:string;
}


export class DetailTransaksiView {

  id_menu: number;
  id_size: number;
  size: string;
  topping: string;
  jumlah: number;
  harga_sekarang:number;
  total_harga:number;
}

export class TransaksiDetail {
  transaksi:TransaksiView;
  detail:DetailTransaksiView[];
  constructor(){
    this.detail = new Array<DetailTransaksiView>();
  }

}

this is my httpoption code

let opt = {
  'Content-Type': 'application/json',
  'Access-Control-Allow-Origin': '*',
  'Authorization' : '',
}
if(this.storage.isStorageAvailable()){
  let data = this.storage.retrieve('user_auth');
  if(data){
    opt.Authorization = `Bearer ${data.token}`;
  }
}
this.httpOptions = { headers: new HttpHeaders(opt) };

what makes the error?