This applies when one person embeds a SharePoint document or list on a Confluence page, and another person who does not have access to that item opens the page.
Instead of the document or list, the macro shows a missing-permission message. This matches SharePoint's own permissions: Each person sees only the content they are allowed to open in SharePoint, so the same page can look different to different viewers.
For how permissions work in general, see How are SharePoint permissions applied in Confluence?