Allowing read-only users to download a document and edit the local copy (via IRM)

I want to share a certain excel database with users on our sharepoint platform.
I have created a document library and applied the following IRM policy on it: 

The users should not be able to edit this file on the sharepoint directory.
Therefor they have been granted only Read permissions.
But they should be able to edit the file once it's downloaded (offline copy).

However, when I'm testing this out a user, I always receive this error upon opening it on my local excel app (reading in the web view is no problem):

My Office account is the same on both the sharepoint environment and my Excel installation.

What should I change in my configuration to achieve this?

Kind regards