Hi Christian,

Thanks for reaching out to us. You can add a custom field to collect additional information from the customers. The Custom Fields feature gives you the option to add more fields to your booking form so as to customize it to best match your business needs. The customer’s first and last name, email address, and phone number are there by default, but with the Custom Fields feature you can add extra fields if you want to ask a customer a question, collect additional personal details, or for any other reason.
For appointments, these fields will appear on the Booking form under the default fields, and once your customer fills them this information will be shown in the appointment information on the back-end.

Please, find more information on this link.