微信小程序上传图片到对象存储

官方给推荐一种方式呗！！

微信小程序上传图片到云对象存储   利用url

总是报错

<Error>

<Code>MalformedPOSTRequest</Code>

<Message>The body of your POST request is not well-formed multipart/form-data.</Message>

<Resource>##########.cos.ap-beijing.myqcloud.com/460/head2.jpg</Resource>

<RequestId>NWE5OGRlOTJfNGEyODVkNjRfMTUwOTVfMjkxNWM1</RequestId>

<TraceId>OGVmYzZiMmQzYjA2OWNhODk0NTRkMTBiOWVmMDAxODc0OWRkZjk0ZDM1NmI1M2E2MTRlY2MzZDhmNmI5MWI1OTI5MWRkM2I1ZDU3ZWE5Y2YzNDYzZTEzY2JlMjU3NDQ0ZjA4ODgyZWI5YjU1MDQ5MDFjZDY4MTAzMjg3ZWM2MTU=</TraceId>

</Error>

不知道什么原因啊！！