Thank you for your response Paul. I've seen your article already and I've also already added the Shopify Buy Button to my product page (see: https://www.annebarlinckhoff.com/shop/amour-botanique-01).
Your URL of your plugin seems to be broken Oops! This page cannot be found. It looks like the word '-plugin' has been removed in your URL. https://sf.digital/plugins/shopify-buy-button-plugin > https://sf.digital/plugins/shopify-buy-button
Anyhow, I found it and noticed:
You must be using a Brine-family Squarespace 7.0 template or any Squarespace 7.1 template.
As mentioned above, I'm using Version 7.0– Wexley family (Wexley template). So would I be able to have your plugin in work? If you can adjust it to the Wexley family too, that be wonderful.