How to make a field mandatory on AP invoice

Hi,

we have a requirement to make supplier tax registration number field mandatory on AP invoice for a BU .

We have created a sandbox and under required field added the expression #{bindings.OrgId.inputValue == id of a particular BU}.

However, under preview mode of the sandbox, we are able to save the invoice without providing any value for supplier tax registration number field .

Is there a way to achieve this?

Version:24A

Thanks.