Only Effective Manager can raise SR for Resource

Summary: Prevent a previously mapped manager to raise a service request for a resource

In SR, a Payee DCL is getting records from a Custom Object. The Payee custom object has several lines of the same Employee but has different Manager indicated by a Start Date and End Date.

Content (please ensure you mask any confidential information):

The requirement is only the current Manager will be allowed to create an SR for the Payee selected. For illustration: 1st record Manager Thom is the manager for March. Now, if Manager Don is logged in and creates a Service Request for Alexander, he/she should not be able to save and be prompted with an error.