Symptoms
When using Exchange as your DataSource, you may encounter the following:
Display panels do not show current meetings or allow "spontaneous meetings."
In Display Administration, rooms show a yellow warning triangle.
Hovering over the warning triangle displays the error: "The server refused the connection. Please verify that the Url is correct."
"Save and Test Connection" within the administration portal shows a successful result, but individual rooms still fail to sync.
Cause
This issue is typically caused by a change in how Microsoft manages Exchange Web Services (EWS) permissions within Exchange Online.
Even if your configuration has not changed recently, Microsoft has updated the requirements for EWS access. For a connection to be successful, EWS must now be enabled at both the Organization level and the individual User/Room level.
If the organizational setting is disabled, individual room settings are overridden, causing the server to return a (403) Forbidden error.
Resolution
To resolve this, you must ensure that EWS is enabled globally for your organisation and also for the affected room mailboxes. For a detailed technical explanation of this Microsoft change and how to manage it via PowerShell, please refer to the official Microsoft documentation:
Note: If you have an Application Access Policy in place, ensure the App ID used for Planner Display is still permitted to access the specific room mailboxes.