curl --request POST \
  --url https://api.siftstack.com/api/v1/calculated-channels:validate-expression \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "expression": {
    "expression": "<string>",
    "channelReferences": {},
    "expressionChannelReferences": [
      {
        "channelReference": "<string>",
        "channelId": "<string>"
      }
    ],
    "functionDependencies": [
      {
        "userDefinedFunctionVersionId": "<string>"
      }
    ]
  },
  "mode": "EXPRESSION_MODE_UNSPECIFIED"
}
'

{
  "error": {
    "errorMessage": "<string>"
  },
  "success": {
    "dataType": "CHANNEL_DATA_TYPE_UNSPECIFIED"
  }
}