Partial is used from EXT:backend/Resources/Private/Partials/MultiRecordSelection/Actions.html
URL
{reaction.name} {reaction.name}
/{reaction.identifier}
curl -X 'POST' \
    '/{reaction.identifier}' \
      -d '{"my-payload":"my-value","field-b":"my-input"}' \
      -H 'accept: application/json' \
      -H 'x-api-key: ***your-secret***'