How to add a specific error message or warning message while submitting a PR based on a value added?

The case that I have a DFF with a list of value, and need to add a validation point on choosing specific values while PR Line Category is "X", and other specific values when for example the PR Line Category is "Y", So I need when submitting the PR to have and error message or warning if I didn't follow the rule that I need to add the validation based on it.