With a number custom field, customers will be required to input a number.
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 enters a number
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. Input the Minimum, Maximum and Default  number value. For example, if you want to let customers input a number between 10 and 50, and show 10 as the default, you will have to set:
- Minimum value: 10
- Maximum value: 50
- Default value: 10
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: