I was wondering if a square developer application could use webhooks to get notified when an item is sold. I don't want to create a new POS, I just want to use the one given on the app store but have the new application be able to access the information through webhooks of the pre-made POS app. The one step I'm confused on is how do I send the curl request and what is that supposed to do. Is there a walk through demonstration on this or just about the Square API. Thank you