Troubleshooting how to implement dynamic reply-to names and addresses

I’ve been following the Marketing Cloud documentation to set up dynamic reply-to names and email addresses with a sender profile as outlined here:

Ampscript for Dynamic reply mail management

I’ve gone through all of the steps – setting up the data extension and setting up the content areas with the Lookup function – but when I attempt to use the ContentArea function in the sender profile fields – I get an error saying the lookup function is invalid. Here’s an example of a lookup function in the content area:

%%=Lookup("z_pw_rep_id_test","RepEmail","RepID",RepID)=%%

I do have advanced sender profiles enabled on my account, so that’s not an issue. Has anyone else attempted this and had success – or used a different approach?

I’ve attached a screen shot of the error I got.