I tried using this
curl -X POST -H "Content-Type: application/json" -d '{ "get_started": {"payload": "qr"} }' "https://graph.facebook.com/v2.6/me/messenger_profile?access_token=myPageAccessToken"
In response I also got { "result": "success" }
But the bot does not show any button.
It was working fine, All I had to do was, deleting the existing conversion.
In my case, get started button only appears, when there's no message exists in past.