getting the "to" correct in a process definition email

Hi all,

I want to send an email to the person who sent in a case when the case has been at status "customer" for 7 days.  I am struggling to get the "to" part correct.  I have another process that is working correctly, and that one has "contacts related to cases : email address" in the "to" section.

But I have no idea how to replicate this in my new process definition.  I've tried everything I can think of from the Recipient section but nothing works.  This is what I see in the process that is working:

Can anyone help?