You have three options to migrate your RDS CALs:
Automatic connection method: This recommended method communicates via internet directly to the Microsoft Clearinghouse outbound over TCP port 443.
Using a web browser: This method allows migration when the server running the Remote Desktop Licensing Manager tool does not have internet connectivity, but the administrator has internet connectivity on a separate device. The URL for the Web migration method is displayed in the Manage RDS CALs Wizard.
Using a telephone: This method allows the administrator to complete the migration process over the phone with a Microsoft representative. The appropriate telephone number is determined by the country/region that you chose in the Activate Server Wizard and is displayed in the Manage RDS CALs Wizard.
Similar discussion here [https://learn.microsoft.com/en-us/answers/questions/295916/migrate-a-few-rds-cals-to-another-server-(-split-r ](https://learn.microsoft.com/en-us/answers/questions/295916/migrate-a-few-rds-cals-to-another-server-(-split-r )
Hope this resolves your Query !!
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