src/Collections/ButtonCollection.php
public function addPostBackButton($text, $payload = '')
    {
        $this->add(new Button(Button::TYPE_POSTBACK, $text, $payload));

        return $this;
    }
public function addPostBackButton($text, $payload = '')
    {
        $this->add(new Button(Button::TYPE_POSTBACK, $text, $payload));

        return $this;
    }
public function addPostBackButton ( $ text , $ payload = '' ) { $ this -> add ( new Button ( Button :: TYPE_POSTBACK , $ text , $ payload ) ) ; return $ this ; }
Add postback button

@param $text
@param $payload

@return ButtonCollection
Add postback button