Option caption will be Current Option's Name if you want it to be Campaign. If you want to display the list of Clients though, you should change the Type of Choices to Client and Search For Campaigns' each item's PartnersId:unique maybe.
@hergin thank you for your reply. OK, I’ll change the Type to Client, you are right.
There are many Campaigns and Clients can be in many of them. So I’m not sure how I should use :unique
I’ve changed the type to Client as you suggested:
My idea is to do a Search in Clients and check if the Client ID is in PartnersID list. But I get error Evaluates to list of Clients but that’s what I want to do…