Slic3r Prusa Edition - Can't set Sequential Printing Priority

I'm trying to use the Sequential Printing Priority feature in Prusa Edition 1.40.1_win64. The user manual states that the priority can be set from the advanced menu in the settings dialog for each item. However, I find that the Priority menu does not come up when I access it. The manual page is attached as well as what I see instead .

I have sequential printing enabled in the Print Settings/Advanced section and I have placed 4 individual items on the plater.

What else, do I need?

Marc