Hi @Farhad Kayani ,
Unfortunately, it is not possible to use a SQL Server 2009 product key for SQL Server 2008. These are two different versions of SQL Server and their product keys are not interchangeable.
For detailed information about the license issue, you can call 1-800-426-9400, Monday through Friday, 6:00 A.M. to 6:00 P.M. (Pacific Time) to speak directly to a Microsoft licensing specialist. Or you can go to Volume Licensing Service Center support. Please choose region/language and choose to call or have web.
Best regards,
Seeya
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