You are trying to configure Microsoft 365 to route emails to Exclaimer, and you encounter the following error message:
Within Microsoft Datacenters, certain objects are consolidated to save space, and when using Exchange Online PowerShell to modify one of these objects for the first time, it is necessary to run the Enable-OrganizationCustomization PowerShell command to allow this. This process is known as hydration.
If you encounter this error, Exclaimer will automatically run the Enable-OrganizationCustomization cmdlet on your behalf. Once the command has been run, it can take some time to fully hydrate the organization. This process is usually completed within 1 hour, but it can take longer in some situations.
After one hour, click RETRY; if you are logging in again, re-run the configuration, and it should go through successfully.
For more information on the error, please see the Microsoft TechNet article.