Hi Kamikun,
Truthfully, PayPal's giving us fits right now. We're not the only ones - I'm reading a lot of complaints on developer boards that it's just not working with a lot of people's carts.
Can you call us? If you talk directly to Lee or Kevin, and tell them what you want, either of them should be able to send you a PayPal invoice for the right discounted amount. Or just fill out the Contact form on our site at:
http://www.iliumsoft.com/site/support/kb/contact.php
and explain what you want. We'll figure out something.
Sorry about the extra hassle!!
Thanks,
Ellen