// Below subscription captures updates to the hold status of units in the yard for a specific steamship line.
{
  "type": "subscribe",			// Required: Don't Change
  "channel": "/nsp",			// Required: Don't Change
  "transport": "ws",			// Required: Don't Change	
  "groupId": "stoppedRoad",		// Required: GroupId is whatever you want it to be. No duplicates, so name accordingly.
  "filters": [  				// Required: Your main filter array. All key:value pairs will go in here.
    {
      "eventName": "Unit",			// Required: Your streamable event
      "operation": "update",		// Optional: Operation mode of the event. create/update/delete
      "changeFields": {				// Optional: Used to filter when certain fields on the eventName record changes. Read page 13 on Developer guide for more details
        "include": ["stoppedRoad"]	// Optional: list of events included
      },
      "filter": {					// Optional: filter payload tag
        "predicate": [
        "predicate": [
          "transitState=S40_YARD",
          "category=IMPRT",
          "eqOwnerId=MAE"
        ],
        "fields": [					// Optional: Your filter attributes. These come from the payload.
          "unitId",
          "impediments"
        ]
      }
    }
  ]
}