Add payload key to MessageEnvelope

schemas/data-ingress/message-envelope.json

@@ -25,8 +25,9 @@
             "type": "string",
             "enum": ["pis", "timetable", "knowledgebase", "darwin_schedule", "darwin_ts", "darwin_ref"],
             "description": "The data type contained in the message.  Currently supported PIS: PIS Data, Timetable: CIF or VSTP Data, Knowledgebase: Station Data"
-        }
+        },
+        "payload": {}
     },
     "required": ["service_name", "service_id", "data_type", "sent_timestamp"],
-    "additionalProperties": true
+    "additionalProperties": false
 }