Zoom won't allow me to write in the email window for scheduling a meeting

When I hit "schedule" on the initial Zoom sign-in window, it takes me to a new window where I can schedule a meeting with a client.  However, once I fill in all the info (date and time and name of meeting), the slot where I write in the client's email address is greyed out and I cannot put an address in it.  Sometimes after multiple attempts, it spontaneously opens, but today it is not.