dynamoDb put item not populating all params

I have 2 lambdas that do the exact same thing, however, they are both written using different langages.

1st lambda - runs on a node.js environment, when I create my arguments to putItem, as follows:

const args = {
          id: "my id",
          __typename: "a type name",
          _version: 1,
          _lastChangedAt: now.toISOString(),
          createdAt: now.toISOString(),
          updatedAt: fields.LastModifiedDate
        }
var recParams = {
        TableName: dynamoTable,
        Key: {
        "id": Id
        },
        Item: args,
        ReturnValues: "ALL_OLD"
      };

and then I use the docClient to insert the row. Everything works fine, all the properties are populated in my dynamo row.

I have the exact same written in Golang:

    item := RecentItem{
    			Id:             "some Id",
    			_version:       1,
                __typename: "a type name",
    			_lastChangedAt: currentTime.UTC().Format("2006-01-02T15:04:05-0700"),
    			createdAt:      currentTime.UTC().Format("2006-01-02T15:04:05-0700"),
    			updatedAt:      currentTime.UTC().Format("2006-01-02T15:04:05-0700"),
    		}
av, err := dynamodbattribute.MarshalMap(item)
input := &dynamodb.PutItemInput{
		Item:      av,
		TableName: aws.String(tableName),
	}

Everything ALMOST works, the item is inserted, but I am missing all the properties except for the id.

Structure declaration :

type RecentItem struct {
	Id             string `json:"id"`
	_version       int    `json:"_version"`
	_lastChangedAt string `json:"_lastChangedAt"`
	createdAt      string `json:"createdAt"`
	updatedAt      string `json:"updatedAt"`
}

Not sure why in Go my dynamoDb row is missing properties. Am I missing something?

Properties other than Id must be exported, i.e, started with an Upper case:

type RecentItem struct {
    ID             string `dynamodbav:"id"`
    Version        int    `dynamodbav:"_version"`
    LastChangedAt  string `dynamodbav:"_lastChangedAt"`
    CreatedAt      string `dynamodbav:"createdAt"`
    UpdatedAt      string `dynamodbav:"updatedAt"`
}