Rollup API won't create when using 1M interval

[Steven_Liu]

Hi,

I am trying to create a Rollup index using below query. However, it kept returning errors. Any ideas??

{
    "index_pattern": "test_index",
    "rollup_index": "test_rollup_index",
    "cron": "0 0/1 * 1/1 * ? *",
    "page_size" :1000,
    "groups" : {
      "date_histogram": {
        "field": "datetime",
        "interval": "1M"
      },
      "terms": {
        "fields": ["cust_id", "type", "status"]
      }
    },
    "metrics": [
        {
            "field": "amount",
            "metrics": ["min", "max", "sum","avg"]
        }
    ]
}

Errors

{
    "error": {
        "root_cause": [
            {
                "type": "illegal_argument_exception",
                "reason": "failed to parse setting [date_histogram.interval] with value [1M] as a time value: unit is missing or unrecognized"
            }
        ],
        "type": "illegal_argument_exception",
        "reason": "failed to parse setting [date_histogram.interval] with value [1M] as a time value: unit is missing or unrecognized"
    },
    "status": 400
}