Trying to add other admin to my FB app

Question

I tried to add another FB user by ID as administrator to my FB app in admin section under

Apps > my-app-name > Developer Roles

and it gave me this error with no explanation

Failed to set access permission for a developer

I got this user's ID by asking him to go to https://developers.facebook.com/tools/explorer and copy-pasting the user hash it returns.

How can I add this user to my FB app with admin role?

Answer 1

It's working now, it was a temporary error.