contacts_events-8.x-1.x-dev/modules/contacts_events_segments/contacts_events_segments.links.action.yml

contacts_event_segment.add_form:
  route_name: entity.contacts_event_segment.add_form
  title: 'Add segment'
  route_parameters:
    contacts_event: null
  appears_on:
    - entity.contacts_event_segment.collection