I got api key,password and signeture from Paypal and set

I got api key,password and signeture from Paypal and set all of them.
and I wrote article and click "pay per view" button.

code was inserted
[ppw id="54335935" description="test" price="100"]test[/ppw]

but in article nothing happend.
what should I do next??

Do you have instruction of this plugin??

Thank you