
Originally Posted by
DrByte
As I said earlier, the ZC PayPal Express Checkout module passes a specific return URL (call it a "callback" or "return" or "cancel" or "whatever", including URLs to ipn_main_handler.php or your index.php or checkout page, or shopping cart page, etc) specific to your store, and this overrides whatever you've specified inside your PayPal account itself. This allows you to have 5000 stores connected to one PayPal account if you wish, and it will notify each one about only the orders that originated from individual stores.
You do have to give your PayPal account "one" URL (to ipn_main_handler.php) just in order to activate the feature in your PayPal account (and that one URL will get notices from all PayPal transactions that don't have a specific IPN URL specified, such as eBay or emailed payments or other stores that haven't implemented the store-specific URL feature that Zen Cart uses). After that Zen Cart takes care of telling it which stores to inform about any updates.
As far as "multiple stores running from one database", which is the real subject of this discussion thread, I'll let others speak to those concerns.