recurring_events-2.0.x-dev/modules/recurring_events_registration/recurring_events_registration.links.action.yml

# Contact registrants button
entity.registrant.instance_contact:
  route_name: entity.registrant.instance_contact
  title: 'Contact Registrants'
  appears_on:
    - entity.registrant.instance_listing
    - view.recurring_events_registrations.event_registrant_list