signal a workflow

Example request

{
  "messages": [
    {
      "channelName": "channelName",
      "value": {
        "data": "data",
        "extStoreId": "extStoreId",
        "extPath": "extPath",
        "encoding": "encoding"
      }
    },
    {
      "channelName": "channelName",
      "value": {
        "data": "data",
        "extStoreId": "extStoreId",
        "extPath": "extPath",
        "encoding": "encoding"
      }
    }
  ],
  "workflowRunId": "workflowRunId",
  "workflowId": "workflowId"
}