mqtt json data

[robbudge]

Anyone any information on JSON formatting for a mqtt subscription.
I am testing MQTT and looking to optimize my PLC Code within Codesys by utilizing JSON.
I can publish and subscribe single tags easily but am unable to extract the contents when i send via JSON.

My Raw JSON is
{"FirstPublish":{"ACV":{"HMI_CMD":12,"PLC_CMD":12,"Valve_Actual":null,"Curr_Setpoint":14,"Mode":6,"Status":null,"Valve_Status":null,"Valve_Namur":null,"Ready":null}}}

When i Subscribe to the topic in 'Raw' format i get the correct JSON Raw Data.
When i switch to JSON and focus on 'FirstPublish' i get [object Object] so far correct and as expected.

The next level expected is to just get [Object] or a value.
I have tried various configurations of FirstPublish:ACV, FirstPublish.ACV etc.... without getting any data.

I was expecting to set an attribute with name
ACV.HMI_CMD from Address FirstPublish:ACV:HMI_CMD
ACV.PLC_CMD from Address FirstPublish:ACV:PLC_CMD