How do I use the Date Reservation Widget

I am creating a form for parents to sign up to visit my classroom to talk about their career(s) to my students.  I am using the widget, "Date Reservation" so that parents can see when someone else has chosen that date (it is no longer available).  The directions of the widget states..."For the widget to work properly, you need to get a Jotform API key from your account settings, so that the widget can reference previous selections and prevent a date from being selected twice."  I've located my API key, but what do I do now.  Where do I paste the API code so that parents can see what date are no longer available on the calendar?

Thank you for your help, Theresa

Once you added the widget. Your API key for that widget should work automatically.

You can do a test submission on your page and select a Date in your Date Reservation widget. After you submit, the selected date you chosen before should be grayed out already.

Means that the widget is functioning correctly.

Thank you Marvin for your help!