If another admin accepted the challenge it's possible that's why it can't be found.
annoying pop up

I am getting this excact same error when trying to accept. This bug prevented my club from participating.
Confirmed that there is some chess.com bug here, for ongoing Arena https://www.chess.com/play/arena/3131073 Team Norway invitation is returning the same error on trying to accept (not ideal to send and accept while Arena is ongoing of course, since the links is gone very fast, but @darkeval was getting the same error even before Arena started, while many other clubs were successfully accepting the invitation without issues).

It seems that it might be connected with bulk invitations of more than 20 clubs per IPL+ owner (who advised to keep the daily limit for inviting to avoid the bug)

i think if you click the settings wheel and then turn off "automatically expand popup notifications" it should stop

i think if you click the settings wheel and then turn off "automatically expand popup notifications" it should stop
That's only available on desktop mode and not the mobile web optimize pop-up toaster alerts.
That said, staff have a ticket in to look into the behavior on mobile web, especially while in games or events

when you go to the settings wheel here, and click it it should remove most of the popups
That is not an option on mobile web when not in desktop mode.

Doesn't the pop-up collapse in a few seconds automatically?
I haven't removed it through Settings because I like to be notified of other notifications [by pop-up] like Daily Match/Game Challenge, Friend requests, etc.

Doesn't the pop-up collapse in a few seconds automatically?
I haven't removed it through Settings because I like to be notified of other notifications [by pop-up] like Daily Match/Game Challenge, Friend requests, etc.
No, it doesn't collapse automatically and in the case of a game, even if it did, blocking the board for even a short time isn't ideal.
Everytime I go to a site on chess.com, I get a pop-up in the corner of the screen saying that a club that I am an admin in has been challenged to a multi-club arena. However, when I click on it, it says that the arena seek was not found. This can be annoying because I have to click the X everytime I reload the page or go to another page on this website because it can be blocking some of the buttons, and overall can distract me. Does anyone know a fix for this?