How can I add external user to a board belonging to an organization

Question

We have a Trello board that belongs to our organization.

Now we would like to add external users to that single board, not to the whole organization. I supposed this should work without problems but when trying to use "Add member". Anyway, I could not find any external users in the search results?

How could I do this (if I know external user's Trello account name) or is it possible?

Answer 1

I wasn't able to search external users with name / trello account but using email address seems to work.