Try going there several times and it should work. I think it may be that the first time anybody connects from another instance to a ‘foreign’ community, it takes time. Given your instance is smaller, newer and literature focused it just means you might be the first person from the instance entering the sub.

This may be the case for many other communities you try and access, so keep an eye out for this.

I’ve just managed to access by spamming it over a minute or two.