Making a form field mandatory based on a previous answer

How can I make arrival and departure fields mandatory only if attendees indicate they have made their travel arrangements on a Dryfta event registration form?

In Dryfta, to require attendees to provide arrival and departure information conditionally based on their response to whether they have made travel arrangements, you should set the arrival and departure fields as mandatory. 

Then, implement logic that displays these fields only if the attendee answers "Yes" to the "Have you made your travel arrangements?" question. Enabling the "Mandatory" option on the dependent fields ensures that when they are visible (i.e., when the attendee has said "Yes"), the form will not allow submission without filling those fields. 

This setup can typically be done in the form builder or field settings by configuring field dependencies and setting mandatory status accordingly.