Payment Integrate In Php

Payment Integrate In Php
Have a php video site and need to add payment system for it.
I atached the script.and its the demo: http://demo.adultwatchscript.com/
when click on video thubmnail for watch, you will se a download link under any video that let visitor to download videos with flv format.
this you need chnage download.php file
I wanna make download just for user that pay.
this paypament system need to be integrate: http://www.daopay.com/developers/how-it-works.php

site admin shoulde have control on price,and also how many video every visitor can download after every payment.
for example 3 or 5 video for 2$ or some thing like this..