Signal k TCP data source ... help please

[garysmith]

I am using the version 1.16.0 of Signal k server.
I've configured a connection under Server/Connections/Add:
The options which I've selected are:
Input type = Signal K
Signal K Source = TCP
I've configured the address & port and the Server makes a connection to a TCP server as confirmed by the connection status on the dashboard.

However the Dashboard indicates zero deltas/second.
The source is converting XDR data and delivering it via a TCP server.
It is being received and logged.
Here is an example of a delta which is being delivered to the Signal K connection.
Can anyone advise why it is not being handled?
I've used the Playground to confirm that the delta format is correct.
I'm at a loss although I suspect that it is something to do with the source section, the significance of which I admit I don't really understand at this point.

Many thanks

{
  "context": "vessels.urn:mrn:imo:mmsi:601270700",
  "updates":
  [
    {
      "source":
      {
        "label": "XDR_Data",
        "type": "NMEA0183",
        "talker": "II",
        "sentence": "XDR"
      },
      "values":
      [
        {
      "path": "environment.outside.air.temperature",
      "value": 279.85
        }
      ]
    }
  ]
}