APEX

I created a set of Wizard pages. The second page contains a user agreement form. I have a checkbox at the bottom of the page that the user must check before they can proceed on to the next page of the wizard. I would like to use the built-in validation that APEX provides, but what Type (ie. PL/SQL Expression, Function Returning Boolean, etc) should I specify, and what expression do I use for the validation.

The checkbox is P19_AGREE, and I tried selecting PL/SQL Expression with an expression of

:P19_AGREE = 'Y'

with the default value of the checkbox set to N.

It doesn't matter if I check or uncheck the box, it won't pass the validation.

Please help.
Thanks,
Kris