You have to be in one of the clubs to participate. Upon trying to join the tournament it should give you a dialogue that requires you to join as a club.
Club Arenas

@Malkolmn: +1
As far as I can see, you've organized an arena for today and finally no one from the participating clubs could join this arena, right ...?

@Malkolmn: +1
As far as I can see, you've organized an arena for today and finally no one from the participating clubs could join this arena, right ...?
Yes, it's right. I happy, that somebody understands me
Tomorrow Arena Kings Club Arena and I don't know when chess.com will corrects whis bug.

I know. So, my Club is organising this tournament. But now it is don't work correct.
I just created one and players from both clubs could join.

@Martin_Stahl: Take a look here:
The button to challenge additional clubs and the Club Standings column both disappeared today. More than fourty clubs have registered in this tomorrow's arena ... and it isn't sure at all, that the members of their clubs will be able to join the Arena tomorrow.#
https://www.chess.com/play/arena/1341639

@Martin_Stahl: Yesterday I've had both as well. They disappeared today.
With more than fourty registered clubs this is already now an unfortunate situation: If I don't cancel the Arena, this might disappoint many players. If I cancel it, it will surely disappoint many players ...
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Hello! Tell me please, when Club Arenas will work without bugs?