Marketpress shopping cart & payment buttons don't seem to work

I have marketpress installed. I’ve entered paypal credentials and published a basic product page.

Like with other plugins, I’m not finding any documentation that addresses the setup of this plugin, so I don’t know what to do other than ask here. There are helpful tutorial videos that outline the features of this plugin, but they all seem to assume that you install the plugin and activate, and it works. That’s not what I’m experiencing.

I have the plugin set up as best as I can tell how to set it up, but when I click the payment button, nothing gets added to shopping cart. I just get forwarded to the home page and nothing happens.

I don’t see a store page or a shopping cart page…do these need to be created manually? What other steps are necessary to get Marketpress to work?

Here’s my goal: I have a page set up here:

There’s a buy button on that page, and I want that buy button to allow a visitor to purchase that product. The product will be delivered to them after the sale. That’s all I’m going for. I’ll only be selling a few things on this site. I’ve tried using a product shortcode on this page in order to initiate the buying sequence, but that doesn’t work either. Any time I test a buy button, I just land on the home page and nothing else seems to happen.

The reason I’m using Marketpress when I could just use a few individual paypal payment buttons is because I’ve been told that in order for Affiliates to properly track sales, I need to have Marketpress installed too. Tracking affiliate sales of this product is important.

The example product page I have set up is here:

Any insight into how I can use this plugin to sell products is much appreciated!