this.vendorProducts.find(..) is undefined

Appflow
#1

I get this error message:

this.vendorProducts.find(…) is undefined

game.html

<ion-item>
      <ion-label>Produk</ion-label>
      <ion-select [(ngModel)]="produk" interface="action-sheet" (ionChange)="changeSelectedProduct(vendor);">
        <ion-option value="Steam"><img src="assets/imgs/game/steam(us).png" width="50">Steam</ion-option>
        <ion-option value="Garena">Garena</ion-option>
        <ion-option value="Playstore">Playstore</ion-option>
        <ion-option value="Gemcool">Gemcool</ion-option>
        <ion-option value="Steamid">Steamid</ion-option>
        <ion-option value="Lyto">Lyto</ion-option>
        <ion-option value="Megaxus">Megaxus</ion-option>       

      </ion-select>
    </ion-item>

game.ts

changeSelectedProduct(vendor) {
    // change selected vendor

    console.log(vendor);    

    this.selectedVendor = vendor;
    this.selectedProducts = this.vendorProducts.find(vp => vp.vendor === vendor).products;
  }

I wonder why? Thanks in advance.

#2

share some more code of game.ts, to figure it out