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{
   "callback:id","DEF123",
   "event_id":"AB234SDFD234",
   "event_type":"subscription_added",
   "event_date":"2017-02-15T15:42:23Z",
   "delivery_attempt":"1",
   "subscription":{
      "person":{
         "id":"ABC123",
         "external_id":"ex1234",
         "url":"/companies/:id/mobiledb/persons/ABC123"
      },
      "subscription_list":{
         "id":"1234",
         "url":"/companies/:id/mobiledb/subscription_lists/1234"
      },
      "opt_in_date":"2017-01-15T15:34:52Z",
      "acquisition_campaign":{
         "id":"2342312",
         "url":"/companies/:id/campaigns/acquisition/2342312"
      },
      "url":"/companies/:id/mobiledb/persons/ABC123/subscriptions/1234"
   }
}