There was an excellent discussion on the subject two months ago and I bookmarked it. Unfortunately it reports "Invalid Operator" error when I try to use that bo

There was an excellent discussion on the subject two months ago and I bookmarked it. Unfortunately it reports "Invalid Operator" error when I try to use that bookmark now. We're looking to hook up a credit card processing to our app. As cheaply and secure as possible :) We're running a subscription-based service therefore a solid recurring billing is a must-have. Suggestions? Feedback on whoever you're using? Thanks!