Access Denied Redirect

Dear Support-Team,
I would like to deny access to the Backend to a specific user group (= subscribers) and instead show a custom message like “This contend is only visible to Premium users”.

I tried to accomplish this by using the “Access Denied Redirect”-option and selected “Show customized message (plain text or HTML)” but when a subscriber tries to enter the Backend the user does not see my custom message.

Do you have any ideas on what is wrong?

Thanks in advance!