how to make paypal discount code?

i know there is a way to do this,but i just cant see it where in paypal..

i have a price set on my site , let say 50$ and i want to create a paypal coupon code,so when they entered ,at check out so they can use it,

and they will get from 50$ to 30$ by using that code,


any advice will appreciate !

thanks

 

Have you tried Google? I put your question in Google and got an answer from eHow.

 

friend,you think i post question here before i do the research?
so if you know ,how to reply here...
thanks