question

You can refer to my testing example code, It will print out the item ID from the currently logged in player's inventory.

 void Start()
     {
         var request = new LoginWithPlayFabRequest { Username = "", Password = "" };
         PlayFabClientAPI.LoginWithPlayFab(request, OnLoginSuccess, OnLoginFailure);
     }
    
     private void OnLoginSuccess(LoginResult result)
     {
         Debug.Log("login successful!");
         TestGetUserInventory();
     }
     public void TestGetUserInventory()
     {
         PlayFabClientAPI.GetUserInventory(new PlayFab.ClientModels.GetUserInventoryRequest()
         {
    
         },
         result => { 
             Debug.Log("Get User Inventory successful");
             foreach (var item in result.Inventory)
             {
                 Debug.Log("Item: " + item.ItemId);
             }
         },
         error => {
             Debug.Log("Got error getting user Inventory");
             Debug.Log(error.GenerateErrorReport());
         });
     }
    
     private void OnLoginFailure(PlayFabError error)
     {
         Debug.LogWarning("Something went wrong with login API call.  :(");
         Debug.LogError(error.GenerateErrorReport());
     }