Squarespace is a beautiful platform, but one of the hardest to use when it comes to Google Shopping feeds for Google Merchant Center. The only real option is to manually create a Google Shopping rather than directly in Squarespace.
This is obviously not ideal because prices can change, inventory can change, and new products can be added, and it is a huge pain to update an excel file every time these changes occur.
Fortunately, there’s hope yet! Feedonomics has an API that lets you easily export your Squarespace feed to Google Shopping, and perform powerful optimizations in the middle. Highly recommended for any Squarespace store that wants to be on Google Shopping, Bing Shopping, or Facebook Dynamic Product Ads.