What is the best way to do payment processing on OS X? : <p>I have seen a million tutorials for Paypal on iOS but I noticed that Paypal doesn't seem to have an SDK for OS X and MAC desktop applications.  I have desktop app that I have built in swift and the time has come for some sort of payment processing.  If I cannot use Paypal then what is the best form of payment processing for non mobile applications? </p>
