Facebook 'Get Started' Button not showing up anymore in my chatbot

Question

I'm not able to see 'Get Started' button in my messenger bot conversation.

But it DID appear. And for some unknown reasons, it disappeared yesterday.

I've already made this request :

POST https://graph.facebook.com/v2.6/me/messenger_profile?fields=get_started&access_token=XXX

{ 
  "get_started":{
     "payload":"getstarted"
   }
}

And checked :

GET https://graph.facebook.com/v2.6/me/messenger_profile?fields=get_started&access_token=XXX

Result :

 {
    "data": [
        {
            "get_started": {
                "payload": "getstarted"
            }
        }
    ]
}

I tried to delete the conversation both on facebook web UI, messenger web UI and iOS app.

I am administrator of that app.

Any suggestion ?

Thanks !