Hi @DLGross,
Could you please share a screenshot of your flow's configuration?
The error message told that there is something wrong with the uri that you provided. The $filter query option is not supported in Get Messages function of Office 365 Service Communications API.
Please modify your URL within your HTTP action as below:
https://manage.office.com/api/v1.0/tenant-id/ServiceComms/Messages?MessageType='Message Center'
Then try your flow again to check if the issue is solved on your side.
More details about the Get Message function of the Office 365 Service Communications API, please check the following article:
Get Message function
Please check and see if the following article would help in your scenario:
https://msdn.microsoft.com/office-365/get-started-with-office-365-management-apis
Best regards,
Kris