question

Please note that the API GetInventoryItems does not support filtering with "FriendlyId". Currently, only 'type', 'id', 'stackId' and 'eq' are supported in this API’s request parameter “Filter”. If you want to use “FriendlyId” to check if a player has a specific item in his inventory, then as a workaround, you can call API GetItems to get the item id through FriendlyId first, then call API GetInventoryItems and filter with item id to check if player has this item. Or you can call the API SearchItems to cache the entire catalog first, then you only need to call the API GetInventoryItems once. In addition, you can refer to Search - PlayFab | Microsoft Learn for more info about using filter. You can also refer to my test code below.

 public void TestGetInventoryItemsAndFilter()
     {
         PlayFabEconomyAPI.GetInventoryItems(new GetInventoryItemsRequest()
         {
             Filter = "id eq 'c41dc5ca-6fbf-4a41-xxxx-xxxxxxxxxxx'"
         },
     result => {
         if (result.Items == null ) Debug.Log("The player does not own this item");
         else Debug.Log("The player owns this item");
     },
     error => {
         Debug.Log("Get error");
         Debug.Log(error.GenerateErrorReport());
     });
     }