如何使用诀窍API获取按月记录？

Question

使用https://www.knack.com/developer-documentation/通过过滤器获取记录。但是我坚持要获取月度记录。下面的演示提供了过去1个月的记录。但是我需要使用哪个运算符来获取月度记录

$data = [
          [
            'field' => "field_28",
            'operator' => 'is during the previous',
            'range' => 1,
            'type' => 'months'
           ]
        ];

        $url= 'https://api.knack.com/v1/objects/object_1/records?filters='.rawurlencode(json_encode($data));