Validate the value selected in Grade Step LOV and throw error or warning based on the selection

Summary:

In the Add Assignment page, customer has Grade and the in Step field we can select values. The current challenge is we would like to build a validation rule to ensure the Grade Step Progression works as expected.

User is allowed to select only couple of LOVs and if they select other LOV values application should throw a hardstop error.

Any inputs on how this can be achieved is highly appreciated.

Action - Add Assignment

Section - Assignment

Field - Step

When we do inspect element - we get field selected as addPersonWorkRelationships.GradeStepId

but in the VBS the attributes we have is Step, Step Name, Step ID, Step Number but even if we select any of these fields the validation is not getting triggered