OpenAPI-Generator (Go Server): Create endpoint which allows file download

Question

I'm using OpenAPI-Generator for Go server: https://github.com/OpenAPITools/openapi-generator, and I'm trying to generate an endpoint which allows file download (excel file to be precise). I checked OpenAPI documentation and based on it I made this endpoint definition:

/v1/address/postcode-ranges:download:
  post:
    requestBody:
      content:
        application/json:
          schema:
            $ref: './schema.yaml#/V1DownloadPostcodeRangesFileRequest'
    responses:
      "200":
        description: Excel file
        content:
          application/octet-stream:
            schema:
              type: string
              format: binary

But instead of creating an file download endpoint, it creates endpoint which returns JSON:

func (c *AddressApiController) V1AddressPostcodeRangesdownloadPost(w http.ResponseWriter, r *http.Request) {
    v1DownloadPostcodeRangesFileRequestParam := V1DownloadPostcodeRangesFileRequest{}
    d := json.NewDecoder(r.Body)
    d.DisallowUnknownFields()
    if err := d.Decode(&v1DownloadPostcodeRangesFileRequestParam); err != nil {
        c.errorHandler(w, r, &ParsingError{Err: err}, nil)
        return
    }
    if err := AssertV1DownloadPostcodeRangesFileRequestRequired(v1DownloadPostcodeRangesFileRequestParam); err != nil {
        c.errorHandler(w, r, err, nil)
        return
    }
    result, err := c.service.V1AddressPostcodeRangesdownloadPost(r.Context(), v1DownloadPostcodeRangesFileRequestParam)
    // If an error occurred, encode the error with the status code
    if err != nil {
        c.errorHandler(w, r, err, &result)
        return
    }
    // If no error, encode the body and the result code
    EncodeJSONResponse(result.Body, &result.Code, w)

}

    docker run $(DOCKER_USER) --rm -v "${PWD}:/local" openapitools/openapi-generator-cli:latest generate \
        -i /local/docs.yaml \
        -g go-server \
        -o /local/_build/go-server \
        --additional-properties=onlyInterfaces=true && \
        cd ./_build/go-server/go && \
        go mod tidy && \
        go fmt ./... && \
        goimports -w .