How to make the "user-responsible" field mandatory in Cost Center Master Data.

Create a Validation regularisation for Cost halfway maestro data.
requirement is to marque "User responsible" tract mandatory. idiosyncratic can't prevention the outgo halfway and alteration the outgo halfway if "User responsible" is blank.

I person created the validation regularisation successful GGB0. 

Prerequisite: SYST-TCODE = 'KS01' AND CSKSV-KOKRS = 'GCON'
Check: CSKSV-VERAK_USER <> ''
Message: Error message; the User liable tract can't beryllium blank.

But its not working.

I person activated the Validation successful OKC7 and GGB4.

Please usher maine however to marque user-responsible tract mandatory successful Cost halfway Master data.