Paypal webpay standart - how to return user to specific URL?

Paypal webpay standart - how to return user to specific URL?

i need after transaction user to get to specific url so he can get what is he paying for. how? there is only

<input type="hidden" name="return" value="sadasdasdasd">
<input type="hidden" name="cancel_return" value="asdsadasd">

but this is not where he get automatically. it's only if he follows return to merchant link.

but possible somehow to send data to my site to activate service for user instantly?

thank you guys for help!