Hi, I need to create a form on my site through which a user may require the administration of the site a number of credit points then find himself in his profile. These points would then credit to buy services from its site through an automated system. I require 30 credits, I pay 10 for a service and automatically in the profile I need to find 20 credits and no more 'as He has climbed those 30 spent. So, not cash payment Example: within the site, find a banner PayPal, click and pay 20 euros. Once you have paid 20 euros to me in the profile are automatically assigned 20 credits. I spend my site and spending are scaled. How can I do?