Avios / AerLingus Booking

Trying to book Chicago-Shannon on AerLingus.

I'm going through the Avios portal and I'm signed in with my AerLingus login info.

I can book a Chicago - Dublin flight without a problem.

However, when I try to type in Shannon into the "To" field, it doesn't give that as an option. I know there IS a Chicago-Shannon flight that day, as I can see it when I look directly at the AerLingus airline page.

Am I doing something wrong?