Purchase two Echo Dot (3rd Gen) - Smart speaker with Alexa - Charcoal Devices [Affiliate Link] for $39.98. It's a BUY TWO GET ONE FREE DEAL. But it could be confusing.
On the product description it says, "Prime members get 2 for $39.98. Enter code DOTPRIME2PK at checkout."
So if you put one Echo Dot into your basket, and checkout with the code, you get an error, "The promotional code you entered cannot be applied to your purchase.
Why?
It's because Amazon isn't going to actually give you two when you ORDER ONE, you have to ORDER TWO, ENTER THE CODE, and then one gets discounted, so the total is $39.98.