error message on appointment page

Hi,

I get this error:

"Warning: Missing argument 3 for App_Membership2::get_price() in /homepages/11/d555116541/htdocs/demo/bypstage/wp-content/plugins/appointments/includes/class_app_membership2.php on line 89"

on my appointment page http://demo.dazonet.com/bypstage/make-an-appointment-3

and on the product appointment page http://demo.dazonet.com/bypstage/store/products/appointment

please advise,

thanks,

David