Single Add to Cart Buttons Placed Elsewhere on Website (not in Store)

I used the shortcode to place a "Add to Cart" Button on a post page, but when I click on it, the item does not show up in the cart widget or on the cart page. What am I doing wrong?

Here's the shortcode I am using:
[mp_buy_button product_id="1" context="single"]

Please help!

Thank you,