Add product to cart with URL parameter - Embed buy button

We would like to add a button to our newsletter campaign that sends the customer directly to the cart page with the product being advertised already in the cart. Is this possible with URL parameters?

I found this example from 2012 that does not appear to work anymore:

from: Add an add to cart button

Still works this way.

My mistakeā€¦i was using the product ID for a product that was no longer active.

Thank you for the quick response!