Add a Channel mention to an adaptive card

I've attempted to build a JSON script to perform this action:

{
    "importance":"high",
    "subject":"This is a mention",
    "body":{
        "contentType":"html",
        "content":"Text goes here. <br/> <at id ='0'></at> <br/><br/>"
    },
    "mentions":[
        {
            "id":0,
            "mentionText":"",
            "mentioned":{
                "conversation":{
                    "id":"0",
                    "displayName":"teamName",
                    "conversationIdentityType":"team"
                }
            }
        }
    ],
    "attachments":[
        {
            "id":"randomKey",
            "contentType":"application/vnd.microsoft.card.thumbnail",
            "contentUrl":null,
            "content":{
                "title":"Test title",
                "text":"textgoes here",
                "buttons":[
                    {
                        "type":"openUrl",
                        "title":"Button",
                        "value":"https://microsoft.com"
                    },
                    {
                        "type":"openUrl",
                        "title":"Button2",
                        "value":"https://google.com"
                    }
                ]
            },
            "name":null,
            "thumbnailUrl":null
        }
    ]
}

The error I receive is:

Method failed: (/beta/teams/) with code: 400

{"error":{"code":"BadRequest","message":"Invalid request body was sent.",