You have a very small store, just 3 products, just 2 products are in stock right now. I think that the vast majority of your customers just purchase one belt. If so, does the shopping cart even make sense? I think no.
Consider removing the ATC button at all remaining just the Buy Now button that redirects users straight to Checkout. Perhaps, if you remove this step altogether, then the conversion will increase.
I noticed that you have free shipping on the store, but there is no notification about it on the sliding cart window. This a big problem because free shipping is a serious advantage to shop from you.
Add a prominent line or test that "Shipping - Free" or "Congratulations! You got a free shipping!" instead of text "Shipping calculated at Checkout"
You have quite a big discount (30%) on all products right now. That's a great advantage for your potential customers and you should remind them about that at every possible place. The sliding cart window is no exception.
Display both original and discounted prices on the sliding cart window. Also, add a savings line in percentage and amount of $ below the prices.
In addition to it, you can add the "You're saving" line below the subtotal, to remind again how much your customers will save if they buy it right now.
I hope these recommendations will be useful to you. Feel free to ask any questions.
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