I didn't know about this issue, thanks for letting me know... I'll be looking at the api when I need to challenge a specific club then!
This Problem Again?

I have no problem to challenge The Square Knights. I think you Stephen and another admin have problems to challenge that club because one of their admins blocked you.
No, it doesn't work that way. Even if a challenger is blocked by one or more admins it doesn't stop the challenge being created.
And when I include double spaces there's no problem.

But i found their club with no problem at all single space or double space. They popped up.
But do you mean in a general club search or when creating a VC challenge? The problem crops up in the VC game challenge page when entering a club to challenge.
(This isn't so much a problem with the site's API as a problem between the way data is represented in club endpoints and club home-pages)
I help run a VC league and we had a strange situation earlier in which one team was unable to find their opponent while setting up their game challenge/seek.
The club is 'The Square Knights' and I was skeptical until I tried sending a VC challenge myself and got the 'No results found' response. It looked like being a problem with the club name and a check of the club's api data showed what it was....
https://api.chess.com/pub/club/the-square-knights
"name":"The Square Knights"
Note the double-space between Square and Knights!
I remember having a very similar problem a few years ago and I was told then that the correct spelling for any club is always as given in the endpoint data. That's fine and dandy if you know your way around the site's api but can't something be done to fix this problem permanently?
It's a hopeless situation for team admins to be copying a club's name into the VC game search field only for it to fail every time without any clue as to why.