I'm wondering how people have used PayPal landing pages with WP. I'm working with the Standard PayPal services at the moment so I've latched onto this explanation that PayPal gives for the &return variable:
'...The URL to which the customer's browser is returned after completing the payment; for example, a URL on your site that displays a "Thank you for your payment" page.
Default: customer is taken to the PayPal website...'
Now lets say I want the customer to be returned to my site (which won't be a problem using the variable mentioned above) and a particular Custom Field value for a post to be updated. In theory I'm thinking I could use that as a way to say "ok this post has been paid for". There will be an &item_number variable that is passed through the PayPal URL that is equal to the post ID I want to ultimately set the Custom Field value of. Make sense? $post->ID value is being passed through the PayPal URL (as &item_number) and I setup my &return variable to go back to my site (all of this has been tested) so then *how* does my landing page grab the &item_number value so it can be used ?