Payload Button

{
  "message":{
    "raw":{
      "attachment":{
        "type":"template",
        "payload":{
          "elements":[
            {
              "title":"A ticket to the theatre",
              "buttons":[
                {
                  "type":"postback",
                  "title":"View this lot",
                  "payload":"@BP:MESSAGE:172240:VARSET:$Confirmedperson|attributevalue"
                },      
                {
                  "type":"postback",
                  "title":"Place a bid",
                  "payload":"@BP:MESSAGE:172240:VARSET:$Confirmedperson|attributevalue"
                }
              ],
              "subtitle":"Did you want to bid?"
            },
            {
              "title":"A £100 voucher",
              "buttons":[
                {
                  "type":"postback",
                  "title":"View this lot",
                  "payload":"@BP:MESSAGE:172240:VARSET:$Confirmedperson|attributevalue"
                },
                {
                  "type":"postback",
                  "title":"Place a Bid",
                  "payload":"@BP:MESSAGE:172240:VARSET:$Confirmedperson|attributevalue"
                }
              ],
              "subtitle":"Did you want to bid?"
            }
          ],
          "template_type":"generic"
        }
      }
    }
  },
  "recipient":{
    "id":"{{1.fbuser.fbid}}"
  }
}