item <-
  list(definition = list(
    container = list (
      type = "hits",
      operator = "or",
      rules=I(list(
        list(value= "test1 test2",
             operator = "contains_any",
             element = "page")))

    )
  ),
  owner="test",
  reportSuiteID="test",
  description="API Generated Segment",
  name="test segment"
  )

> jsonlite::toJSON(item, pretty = T, auto_unbox= T)
{
  "definition": {
    "container": {
      "type": "hits",
      "operator": "or",
      "rules": [
        {
          "value": "test1 test2",
          "operator": "contains_any",
          "element": "page"
        }
      ]
    }
  },
  "owner": "test",
  "reportSuiteID": "test",
  "description": "API Generated Segment",
  "name": "test segment"
}

> jsonlite::toJSON(item, pretty = T, auto_unbox= T)
{
  "definition": {
    ...
  },
  "owner": "test",
  "reportSuiteID": "test",
  "description": "API Generated Segment",
  "name": "test segment",
  "id": "s1982XXXXXXXXX_XXXXX_XXXXX",
}