With a checkbox custom field, customers will be required to tick a checkbox, for example, to answer a question.
1. Go to Settings>Customer Details
2. Go to the Custom fields tab
3. Click on the New field button
4. In the Type section, from the Type  scroll down menu, select the user checks/unchecks a checkbox
5. In the Application section, tick the customer making the booking  and/or to the participants  checkboxes to set when the field should be applied
6. In the Details section, input the Name  and Description  of the field.
7. Tick the Default value  checkbox if this field is checked by default when customers make a booking.
8. Tick the Public  checkbox if customers can see this field.
Custom fields for participants will be asked during the booking process if you set that you want to Ask for the details of every participant: