Well joining means registering, having a signon/logon to connect to the reader. I pay through paypay with Keen, but I had to register with Keen first. Keen also takes direct cc payments too.
btw, Keen has changed something with Paypay (I noticed it about 6/8 mths ago), because when you add money now, it's almost instant when you use paypal - it doesn't go through paypal first where you log on and confirm that you are, who you say you are.
I wonder how they are doing that now?