"Book a session" button not working

Currently, on https://languagelab.be/ (after login), button "Book a session" (e.g. <button class="button float-start " data-cal-link="https://cal.com/sbibauw/tutorat-en-francais?email=s@e.com&amp;name=A supprimer">Réserver une session</button>) does not do anything.

Should it be removed? Or another solution to schedule new sessions with an existing tutor? At least an indication for users to contact their tutor?