Json object array issue

I am not able to show using ngFor in front end
of this value

{"orderId":"5919930bbd9d5b6093b855ca","_id":"591ade3b07739320890249b5","GrandTotalAmount":26375,"productDetails":[{"productCatalogId":"58ff187cd753ba37ed752308","productName":"samrat","productModel":"smc","productVersion":"1.0","productLangauge":"English","productMrp":5275,"productDiscountPercent":0,"productDiscount":0,"productSalePrice":5275,"productQuantity":5,"productTotalAmount":26375,"_id":"591ade3b07739320890249b6"}]}

this is my service.ts code

getmycart(orderid){
      var headers = new Headers();
      headers.append('X-access-token',`${this.auth.getToken()}`);
      return new Promise((resolve) => {
          this.http.get(`${Contants.API_CARTPRODUCT+orderid}`,{headers:headers}).map(res=>res.json()).subscribe((data) => {
              this.result = data;
              resolve(this.result);

          })
      })

  }

this is my .ts code

 loadMycart(){
    let listnow = this.authuser.getmycart(this.orderId);
    console.log(listnow);
       listnow.then(data => {
       this.result=data;
       console.log(this.result);
         })
  }

this is my .html code

<ion-content padding>

  <div *ngFor="let j of result.productDetails">
    {{j.productName}}
    {{j.productName}}
    {{j.productVersion}}
    {{j.productLangauge}}
</div>
</ion-content>