Prohibit User Self-Approval - How to make the setup of the payload attributes?

Summary:

Prohibit User Self-Approval - How to make the setup of the payload attributes so it is being assigned to the users Line Manager?

It's for the rule; ProjectStatusNotificationApproval.

The rule look like this:

I need help to how I can setup the payload attribute under Prohibit User Self-Approval, so it can be assigned to the DTU Project controllers Line Managers when the DTU Project controllers project status change themselves.

I have tried to put in the task creator in the expression but it comes up with this, when I try to save:

Best Regards,

Liaqatulla Safi