25C - RSSP - Product Details Validation Rules

Summary:

Hello,

In the extensibility capabilities for RSSP 25C, the Product Details page is marked as supporting Validate Field Values:

However, when we try to configure any validation rules for this page they do not take effect.

What we are trying to do is control which source organization (the "Supply Source" field) a user can order material from via an IMT to Expense. As we cannot directly do this (as Procure from Preferred Sources is turned on), we are attempting to use a validation rule like so to stop them:

We also tried "Source Organization Initial Value" and nothing happened.