Received an error period is not closed for Cost Management

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Dear ,

I received an error when GL period is closing. i received error the Aug-21 period is not closed for Cost Management 

Kindly guide me how to closed Cost Management period current period Sep but how i closed Aug-21 period is not closed for Cost Management 

I also tried cost Accounting > Manage Cost Accounting Period > In there option to close current period (Sep 21) But Not Prior Period (Aug 21)

Thanks