curl -X POST
  https://www.exacttargetapis.com/data/v1/async/dataextensions/key:my_external_key/rows
  -H 'Authorization: Bearer my_access_token'
  -H 'Content-Type: application/json'
  -d '{
    "items":[{
        "Email":"myname@company.com"
    }]
}'

{
    "requestId": "1b6f96ce-66e2-451a-9a21-f53f8d8f6b3d",
    "resultMessages": [
        {
            "resultType": "Operational",
            "resultClass": "Error",
            "resultCode": "CustomObjectNotFound",
            "message": "Failed to resolve the Custom Object from the provided ObjectReferenceIdentifier [Id: Null, Key: mics_test]."
        }
    ]
}