Looks like existing Moon cards did stop working. Someone got an update from Pay With Moon's customer support:

So they're not going to say it outright, but it's pretty obvious they lost their card provider. On the same day as Jan3 lost theirs. It would be interesting to know if this happened because they had the same provider, which got enough and canceled them both on the same day, of if there's a wider crackdown going on. I'm guessing the former, since I haven't heard of more cases.