how to prevent techicians from assigning tickets to techs that are on pto or leave?

how to prevent techicians from assigning tickets to techs that are on pto or leave?

Your Leave scheduling works if tech creates a NEW ticket and assigns to tech on pto, and then it auto in-assign.

However, if tech assigns existing tickets to techs on pto, it goes thru..   

How to prevent techs from assigning existing tickets to techs on leave status?

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