Help in PayPal PHP Algorithm

I want write a PHP registry code That when a User regi开发者_JS百科stried than go to PayPal site and give some money to us and after her payment , her account activation in our site Automatically . what am i going to do ? Thanks in Advance .

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Check out Paypal's Payflow Link : https://cms.paypal.com/us/cgi-bin/?&cmd=_render-content&content_ID=developer/howto_gateway_payflow_link

The user on your website clicks the Paypal buy button, gets transferred to Paypal to do their payment, and then returns to your website (wherever you specify) to finish.

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Look into Paypal's IPN functionality.

Here is the link to Paypal's IPN PHP API setup that they provide. There should be plenty of snippets / tutorials available from Google though.

EDIT

Also a great resource is http://developer.paypal.com it gives you access to a sandbox to setup test accounts with money etc to test the functionality of your newly implemented system before you send it live.