Tago Message format

Is there any documentation for message format that Tago accepts? It does enforce a tag called “variable” but other than that it appears to accept any valid JSON, however the fields other than a few (such as value, time, location etc.) are not persisted.

An example I tried:

{ "variable":"dummy",
  "value": [
           "deviceid": "device 1",
           "updated": "2020-09-23T20:41:46.966Z"
           "deviceid": "device 2",
           "updated": "2020-09-23T20:42:46.966Z"

This persisted successfully, however, not sure why I can not retrieve the objects under the value tag.