Hi @JOE TAM ,
- First confirm with you whether the DC in the same site as the Exchange server is the schema master?Please check via SetupAssist script.
- If not, The schema, AD and domains can be prepared directly in the site where the schema master resides.
- Or you can move the role to the current site's server. Then run the /PrepareSchema, /PrepareAD, and /PrepareDomains commands from the command prompt and wait for AD replication to complete.
Note that your account needs to be a member of the Schema Admins and Enterprise Admins security groups to prepare the schema.
Please follow the steps in the article: Prepare Active Directory and domains for Exchange Server.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.