Hi! The error is related to calendar integration, and implies that their authorization has expired. This does not explain why they do not see the clients and projects you have setup.
Can you ask them to verify the organization name they see in the top left corner? It should match what you see, as should the organization and workspace ID in the URL when they go to the Reports pages. If not, ask them to click in the workspace switcher in the top-left corner, then change to your organization/workspace. If they do not see it, it means they have not accepted the invite yet.
