How do I grant a GitHub organization access to Netlify CMS?

Our private repository is at GitHub within an organization. All settings in config.yml correct - if we want to connect, we get:

Repo “our-organization/repo” not found
Please ensure the repo information is spelled correctly.
If the repo is private, make sure you’re logged into a GitHub account with access.
If your repo is under an organization, ensure the organization has granted access to Netlify CMS.

How do I grant the organization access to Netlify? Can’t find anything about this task or about the error online.

Follow this guide: