It looks like they turned that feature off.
See https://developer.linkedin.com/support/developer-program-transition
New requirement for Companies API
All calls to Companies API endpoints will require the authenticated
user to be flagged as an administrator of the LinkedIn Company Page
that is the target of the API call. You become the administrator of a
page when you create it. If the page already exists, you will have to
contact the existing administrator to grant admin access to other
LinkedIn members.Your API call will return a 403 Forbidden error if you do not have the
appropriate admin permission to interact with the target company.
And in the first line,
On February 12th 2015 we announced a series of changes to our
developer program. These changes have now begun to take affect and
will be rolled out to the entire LinkedIn application base between May
12th – May 19th, 2015.
So we are out of luck.