"Search" didn't find anything here about the closing of this long time payment handling system in July (2016). I've used
Kagi many times when paying for software from Mac devs. I first got news on another forum that discusses a Mac only app, guess I failed to mention it here. Here's a story in the most recent
TidBITS newsletter about this sad event.
I used it too - it's a very sad tale. Lots of further info in the comment section from devs and customers - definitely worth a read.