I have been developing a website with PHP in which users will subscribe and pay their subscription fees monthly to resume their memberships. To do this, I created a Subscribe button from PayPal and tested it with sandbox, I can receive the payment. However, I couldn't find a way to determine which user have subscribed.
Here is the HTML code for the PayPal button:
<form action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post">
<input type="hidden" name="cmd" value="_s-xclick">
<input type="hidden" name="hosted_button_id" value="BUTTONID">
<input type="image" src="https://www.paypalobjects.com/en_US/i/btn/btn_buynowCC_LG.gif" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!">
<img alt="" border="0" src="https://www.paypalobjects.com/en_US/i/scr/pixel.gif" width="1" height="1">
</form>
As you can guess all users have unique IDs, I want to pass this unique ID to the PayPal page where payment is done then PayPal will pass this ID to me again, therefore the users account will be activated.
I have been searching for this for a very long time. There are many tutorials to do it with IPN but I can't see where to send the user id as an IPN parameter. I haven't managed to use PayPal APIs since their documentation is totally crap.
Maybe someone can give a link with a complete tutorial for this, or tell me what I understood wrongly?
Thanks
As far as I know, you can add up to 255 bytes of data to field labeled CUSTOM in just about every request to PayPal. PayPal returns this field in its responses and IPN's.
For something like subscriptions, I would recommend you to checkout the recurring payment mechanism offered by PayPal via NVP and SOAP. It is not that easy as just generating a button and placing it on your website but since you already wrote an entire website in PHP, you will not have any problems coding it. Recurring payments should provide everything you need to let your users subscribe and pay a monthly fee, including the ability to track who is who.