Getting the Assignee email in a custom field

[Mory Soan]

I have a custom field called "Invitation" where I want to be able to select the current Assignee's email and other Manager ObjectType to send them an invitation.

My current Filter is as follow:

Filter Scope (IQL): ObjectType=Manager

Filter Issue Scope (IQL): Key IN (${customfield_21145.key${0}}) OR ${Assignee}

It is not giving me the assignee's name.  Should I be adding a Filter Scope Assignee?

Thank you