How to send instant reply for some message on mattermost channel

I have a problem with automatic generator of response via mattermost. To simplify a question- I have some dedicated channel on mattermost and if a message send by me is correct I want to have automatic answer “OK” + my_message. Right now I am checking a message and if is good making:

result = {"channel" = "@username",
"text" = "OK" + my_message}
return HttpResponse(result, status=200)

but it doesn’t work. Code is of course in Python and server is standing on Django. Ideas?