Great question — answering as the UphillTech team:
Okay, I've come up with a couple possible solutions. DEALING WITH PAYMENT VERIFICATION WooCommerce's Paypal Standard gateway actually has support for Paypal's IPN service built right in to it. You'll want to use that regardless of the 'hook' route you choose. HOW TO SET UP PAYPAL IPN Paypal IPN is connected to whichever account is the receiver of the money. For example, if you're getting paid at myemail@gmail.com, then you need to set up IPN with that account. All IPN is, is Paypal sending out a "Payment Complete!" (of sorts) notification to the URL of your choice. In order to choose the url that you want Paypal to send the notice to, you need to do these steps: Log in to Paypal Click on...
Full answer by Pete: https://stackoverflow.stackexchange.com/a/28224558 (CC BY-SA 3.0).
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