How to setup USPS Flat Rate Priority Boxes only

-- url of the page with the problem -- : www.brewtroller.com
-- HikaShop version -- : 2.4.0
-- Joomla version -- : 3.
-- PHP version -- : 3.3.6
-- Browser(s) name and version -- : Chrome

I want to setup shipping method for USPS Priority Flat Rate, but its not working. It seems to always pick the same shipping cost regardless of the number of items I put into the cart.

Can anyone guide me?

Hello,
Can you please also show me how did you configured the product that you are using on your cart to test it, so that I can directly test it on my end ?
Thank you.

I've attached screenshots of the weight / dimensions of the 2 products I've been using.

Hello,
I just tested it with on my end by using a product with the same size/weight and also by using your USPS credentials through my USPS shipping method, and it worked fine (the shipping price was changing).
If you still have that issue, can you give me a temporary access to your back-end so that I can directly test it on see from where your issue is coming ?

I just looked at the config I sent..

What I'm trying to do is force flat rate box. So if you change container to flat rate box, you'll see that the rate never changes.

I'd be happy to give you backend access if that would be helpful.

Hello,
Sure you can send it to me through a private message !

PM sent

Hello,
I just tested it on your website with the "2 Way Motorized Ball Valve" product and it worked fine, the shipping method was displayed and the price was changing.