How can you require Candidate Disposition Reason when Rejected or Withdrawn?

Summary:

When we manually move a candidate to either "Rejected by Employer" or "Withdrawn by Candidate" state, we need to ensure there is a disposition reason always being selected. Right now, because the reason field isn't required it is getting missed.

We have Redwood enabled and are trying to explore what options we have in VBS to require this field but so far, not finding how we can make this field required, or unable to define a validation rule. Have others implemented this? If so, what was your approach?

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