DynamoDB error: The provided key element does not match the schema

I know there are so many similar questions about the error, but I tried my best to search them only to find no answer to my question.

I have created a table in dynamoDB, with a partition key named "token", no sort key.

Then I want to update item (insert a new one if not exists) in lambda function. My source code is like this:

docClient = new AWS.DynamoDB.DocumentClient({region: region});
let params = {
    TableName: table_name,
    Key: {
        token: token
    },
    UpdateExpression: "Set xxx = :xxx, yyy = :yyy",
    ExpressionAttributeValues: {
        ':xxx': xxx,
        ':yyy': yyy
    }
};
await docClient.update(params).promise();

I have checked that the table name and the key is correct, but I keep getting the error: The provided key element does not match the schema.

This code works good in develop env, so I get confused why it failed in production env.

It is difficult to add a sort key, so I did not change the table itself.

I tried creating a dummy record with the same attributes, it did not work.

I output the params before docClient.update(), it was like this:

{
    "TableName": "the_table_name",
    "Key": {
        "token": "this_is_1_token-with-alphabet-number-hyphen_underline"
    },
    "UpdateExpression": "Set xxx = :xxx, yyy = :yyy",
    "ExpressionAttributeValues": {
        ":xxx": "some_string",
        ":yyy": "another_string"
    }
}

I'm writing this as an assumption awaiting your response to my question. As you are using the AWS.DynamoDB.DocumentClient it expects your values to be in native JSON format. So I assume you are passing in the low level DynamoDB-JSON format like below:

Key: {
        token: {"S":"some-token"}
    },

Whereas you should be using the following:

Key: {
        token: "some-token"
    },

If my assumption is incorrect, the next check I would do is the data type, be sure you are passing in the correct data type for token as the DocumentClient infers the data type directly from javascript.

Next, I would do a DescribeTable API call and look at the Keys in the output, be sure there is no trailing/leading white space around the key name, for example: token or token .