How to access attribute of member selected on form

@WITHATTR(&quot

Summary

Need to use attribute of member selected on form to perform actions on all other members with the same attribute

Content

Does anyone know how we can use the attribute of a member selected on a form to then perform actions on all other members with the same attribute value?

This FIX works (sample with attribute hardcoded):

FIX(@WITHATTR("Client", "==","Client_1234"))

But this doesn't

FIX({EntityForm})
   FIX(@WITHATTR("Client", "==", @ATTRIBUTESVAL("Client")))

 

Basically we are trying to create a list of all the Entities that share the same attribute as the one selected on the form.

 

Appreciate any ideas/suggestions