How to create a validation message for empty attachment

Summary:

Navigation: My client Group > Workforce Structure > Request a New Position

We want to force users to enter an attachment on the section "Position Details"

by default oracle does not let us to override this property to "Required"

Content (please ensure you mask any confidential information):

We have configured a validation rule but the error message does not display

Preview no validation message:

Version (include the version you are using, if applicable):

25B

Code Snippet (add any code snippets that support your topic, if applicable):