Cannot evaluate expression using Toolbox


I am sure this is a trivial question, but I spent an embarrassing amount of time on it and couldn’t figure it out.

I am trying to evaluate the simplest expression e.g. 7 in toolbox expression, but nothing is displayed.

My webpage should display 7 = 7, where the second 7 is an expression. However, only 7 = is displayed.

bubble editor:
bubble app: