Symptom:

After the buy or enroll button is clicked, a prompt to put in a coupon code appears, then a blank window appears, and nothing else happens.

Background:

Due to the way that PayPal built their integration, the LMS requires the use of a pop-up window in order for the purchase to be made through PayPal. The browser has a pop-up blocker enabled that is blocking that pop-up window from appearing.

Resolution:

Either enable pop-ups in your browser, or click the blocked pop-up icon at the top of the browser window, usually in the URL box, and select "Always allow pop-ups from..." for the site. Then re-load the page and click the buy or enroll button again.