Hello @Mary MBC ,
Welcome to our forum!
According to the error message you provided, it is recommended that you first use this command in Powershell to check the dehydrated state.:
Get-OrganizationConfig | FL IsDehydrated
True means organizational customization hasn't been enabled yet, while false means it has been enabled. If the result is true, your exchange online organization is dehydrated and used the consolidated exchange online setting configurations, then you have to enable organization customization.
To enable organization customization using PowerShell, please connect to Exchange Online first. And then, run the following command to enable the customization of the organization:
Enable-OrganizationCustomization
In addition, when running this command, if you receive the error message, " Enabling customization is not allowed because the organization is currently being upgraded", you may need to run Enable-OrganizationCustomization several times.
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