Unity Facebook Canvas Inapp Purchase Error

Question

I've been trying to make the facebook canvas inapp api working for my game virtual items for quite some time without any success. Its unity made game running in facebook canvas iframe with WebGL.

I am using the following code to make the transaction...

FB.Canvas.Pay (product: "productID",
            quantity: 1,
            callback: delegate(IPayResult response) {
                Debug.Log (response.RawResult);
                if(onProductPurchasedSucceed != null) {
                    if( response.ResultDictionary["status"] == "completed"){    
                        onProductPurchasedSucceed("productID");
                    }
                }
            }
        );

When I invoke this method from canvas page.. This is what I ended up with

Since its a simple game I chose facebook hosted feature to upload my game assets. I have no idea what to fill in App Domains field. I tried to setup apps.facebook.com, but its not accepting