It has a join button, but when you click on it, it apologizes but the community is currently full .
And congrats. I already had proof that the smaller ones do pay, though - I've won 100$ from one a few months back, and 25$ from another one the next month, and I just won another 100$ from one this month (it hasn't paid yet, but it's a different forum from the same market research company that sent the first 100$, so I'm confident it will.) The little ones totally do pay (though to be fair, those were all Amazon, not paypal) - just the big public ones I don't believe actually pay anyone from their sweepstakes, at least not consistently .
I'm on a couple other little invite-only sites that pay raffle tickets rather than guaranteed cash, that I haven't won from yet, but after I won on that first one and it paid without issue, it made me a lot more willing to accept further such invitations.