Paypal Paymentin Fix. Joomla php (alphauserpoints)

for some reason when i buy points with teh alphausr plugin its giving me an error after i come back from paypal. i have changed the settings on paypal for this to work without any problems.. but for some reason its not having it!! i need instant hekp plz... i will chose winner in next 20 min. .. i need to to be done strait away plz... max pay $30