To be able to the Shopify widget in order to embed products or buy buttons right into your Popups or pages, you need to install this FREE app on your Shopify store by clicking on the green "Get" button.
Once installed, it can be accessed from
Then, you select the product for which you want to generate the Buy Button,
After that, you customise the look and feed of your buy button widget, then you click on "Generate Embed Code"
A popup window will be opened to you with your Embed Code, copy it, and head to the popup editor, go to your Shopify widget options, in the settings tag, paste your code in the "Embed Code" option, and it is done, your designed widget/buy button will appear right away.