When trying to access via the app or webapp I get the message: "We're improving your experience. Please log in later".
But I have received no emails regarding an upgrade or something to that effect, and their status site says: Our deliverables will be deployed during second weekend of every month. It may cause some latency in APIs during the deployment window.
1) There are at least a couple YCcombinator startup that does collections: Domu and Respaid.
2) There was a time in a prior life when I did consulting, and of course I experienced the same issue. I re-wrote my contract to get paid in advance each and every week (seldom every month). If I had no payment in my bank, no work that week. Easy, simple, the client was always in control.