Hasura query action exception

Got a small problem (I guess). I created c# rest web API on docker swarm environment. Rest API is working properly - tested via the postman. Then I tried to compose Hasura service on the same docker swarm environment. The console is working properly also. The problem is with query action.

Code:

Action definition:

type Query {
  getWeatherForecast : [WeatherForecastResonse]
}

New types definition:

type WeatherForecastResonse {
  date : String
  temperatureC : Int
  temperature : Int
  summary : String
}

Handler:

http://{api ip}:{api port}/WeatherForecast

While trying to execute query:

query MyQuery {
  getWeatherForecast {
    temperature
    summary
    date
    temperatureC
  }
}

All I got from response is error with json:

{
  "errors": [
    {
      "extensions": {
        "internal": {
          "error": "invalid json: Error in $: not enough input",
          "response": {
            "status": 405,
            "body": "",
            "headers": [
              {
                "value": "Mon, 14 Jun 2021 13:54:00 GMT",
                "name": "Date"
              },
              {
                "value": "Kestrel",
                "name": "Server"
              },
              {
                "value": "0",
                "name": "Content-Length"
              },
              {
                "value": "GET",
                "name": "Allow"
              }
            ]
          },
          "request": {
            "body": {
              "session_variables": {
                "x-hasura-role": "admin"
              },
              "input": {},
              "action": {
                "name": "getWeatherForecast"
              }
            },
            "url": "http://{api ip}:{api port}/WeatherForecast",
            "headers": []
          }
        },
        "path": "$",
        "code": "unexpected"
      },
      "message": "not a valid json response from webhook"
    }
  ]
}

I got desired response by using postman white calling: http://{api ip}:{api port}/WeatherForecast (GET method)

Where should I improve, to finally get desired result from rest api?

P.S. hasura version: v2.0.0-alpha.4 (tried also with v1.3.3)

UPDATE: Released a new version of web API. Inside WeatherForecastController included a new method with POST attribute. Query remained the same, but now graphql query returns what I want.

So the question is: Is it possible to call/access web api methods with GET attribute with Hasura action query?