Array Array of type Observable [closed]

I'm developing an app and need to iterate through an array of Observable-type arrays coming from the firebase. I have the code below but it does not work and it gives me an error. Can someone please help me?

<div *ngFor="let products of categorie | async">
  <div *ngFor="let product of products | async">
    {{product.name}}
  </div>
</div>

categories.ts

categorie: Observable<any[]>;                                 
this.categorie = this.userDatabase.list(this.PATH)
  .snapshotChanges()
  .map(changes => {
    return changes.map(c => ({ key: c.payload.key, ...c.payload.val() }));
  });

ERROR Error: InvalidPipeArgument: '[object Object]' for pipe 'AsyncPipe'