The PayPal module allows you to set up paid courses. If the cost for any course is zero, then students are not asked to pay for entry. There is a site-wide cost that you set here as a default for the whole site and then a course setting that you can set for each course individually. The course cost overrides the site cost.
Template:Moodle 1.8 If you are using Moodle 1.8 or later please verify the default encoding in your PayPal business account. Login go to your PayPal account, select My Account tab, then Profile tab, click on Language Encoding in the right column Selling Preferences. Click on More Options button and select UTF-8 encoding for both cases. If you are using other software with IPN please check that it is compatible with UTF-8 encoding.