Can't create an organization using a name that appears to be available

I was hoping to create a team/organization through https://github.com/organizations/plan but when trying to use the account name I want (e.g. example-org) it states that the name is already taken. The strange thing is that visiting https://github.com/example-org returns a 404 when using the account name I’d like to use.

Any ideas?

I’m don’t know how the page https://github.com/example-org looked when you visited, but for me it looks like this now:

Which shows that the organization with name example-org is taken, it only hasn’t any public repositories yet (but it may have private repos etc.).

When you request a profile page of some organization that really doesn’t exist, GitHub shows a proper 404 page as expected (e.g. https://github.com/not-existing-organization):

The example-org was an example. I’m seeing the 404 page for the organization name I’m actually trying to register but the form doesn’t let me register it.