Elasticsearch 6：无法用毫秒解析日期

I'm generating the date via php using the Chronos library. It's using the formatting syntax php uses. Elasticsearch is version 6.2.4. To connect with the ES server I'm using Elastica. I keep getting this error:

failed to parse [created]

when sending this date:

// 2019-08-14 08:40:05.887179
Chronos::now()->format('Y-m-d H:i:s.v');

This is my mapping

"created": {
    "format": "yyyy-MM-dd HH:mm:ss.SSS",
    "type": "date"
},

In the log of the ES server I see this:

java.lang.IllegalStateException: Can't get text on a START_OBJECT at 1:207

If I change the date format to

// 2019-08-14 08:40:05.887179
Chronos::now()->format('Y-m-d H:i:s.u');

I'm getting this error:

java.lang.IllegalArgumentException: Invalid format: "2019-08-14 08:45:35.809896" is malformed at "896"

So how can I get the milliseconds right? :( I don't mind the format as long as I can store the milliseconds somehow.