Viber Rest Api Cannot open Internal browser

I'm writing a Viber "keyboard" and I want to create a button which opens a link in the internal browser, which according to this doc doc should be done by sending JSON post to https://chatapi.viber.com/pa/send_message . I'm setting buttons' parameters "ActionType": "open-url" and the "ActionBody":"example.com". The parameter "OpenURLType": "internal" is optional and its default value is internal. No matter what I write as value of this parameter, or if I omit it the response is successful, but the url opens in an external browser.

{
    "receiver":"some hash",
    "keyboard":{
      "Type":"keyboard",
      "DefaultHeight":false,
     "Buttons": [
            {
                "Columns": null,
                "Rows": null,
                "BgColor": "#7eceea",
                "Silent": null,
                "BgMediaType": null,
                "BgMedia": null,
                "BgMediaScaleType": null,
                "ImageScaleType": null,
                "BgLoop": null,
                "ActionType": "open-url",
                "ActionBody": "https://www.wikipedia.org/",
                "Image": null,
                "Text": "open this ",
                "TextVAlign": null,
                "TextHAlign": null,
                "TextPaddings": null,
                "TextOpacity": null,
                "TextSize": "small",
                "OpenURLType": "internal",
                "OpenURLMediaType": "nulll",
                "TextBgGradientColor": null,
                "TextShouldFit": null
            }
        ]
   }
}

and the response 200 OK

{
"status": 0,
"status_message": "ok",
"message_token": 5469236575712199350,
"chat_hostname": "SN-CHAT-01_"

}

When I played around with the other optional parameters I noticed inconsistency. Some of them produce an error when you give some gibberish value (like setting the ActaionType to "operghj"). Other optional parameters don't. For example

{
    "status": 3,
    "status_message": "keyboard is not valid. [instance value (\"operghj\") not found in enum (possible values: [\"reply\",\"open-url\",\"\"])]",
    "chat_hostname": "SN-CHAT-01_"
}

Does anybody has any idea how to fix this or what I'm doing wrong?

The parameter "min_api_version": 7 , has to be added to the json, in order to open the url internally.

{
    "receiver":"some hash",
    "min_api_version": 7,
    "keyboard":{
      "Type":"keyboard",
      "DefaultHeight":false,
     "Buttons": [
            {
                "Columns": null,
                "Rows": null,
                "BgColor": "#7eceea",
                "Silent": null,
                "BgMediaType": null,
                "BgMedia": null,
                "BgMediaScaleType": null,
                "ImageScaleType": null,
                "BgLoop": null,
                "ActionType": "open-url",
                "ActionBody": "https://www.wikipedia.org/",
                "Image": null,
                "Text": "open this ",
                "TextVAlign": null,
                "TextHAlign": null,
                "TextPaddings": null,
                "TextOpacity": null,
                "TextSize": "small",
                "OpenURLType": "internal",
                "OpenURLMediaType": "nulll",
                "TextBgGradientColor": null,
                "TextShouldFit": null
            }
        ]
   }
}