Dropbox notification not invoke Lambda

I send back to dropbox the expected Response according to the documentation. In the dropbox app seems Enabled like if it received the right Response. but only works for the initial validation. Then I modified some files to trigger the webhook but Lambda not receive the notifications. I looked in CloudWatch but nothing appear. I tested in CloudFunction and it receive the notifications. This is my code:

import json
import boto3

s3 = boto3.client('s3')

def lambda_handler(event, context):
    bucket = 'evdaas-datalake'
    filename = "test.json"
    uploadByteStream = bytes(json.dumps(event).encode('UTF-8'))
    
    s3.put_object(Bucket=bucket, Key=filename, Body= uploadByteStream)

    
    if (event['requestContext']['http']['method'] == 'GET'):
        return {
            'headers': {
                'Content-Type':'text/plain',
                'X-Content-Type-Options':'nosniff'
            },
            'statusCode': 200,
            'body': f"{event['queryStringParameters']['challenge']}"        
        }

Your code looks correct. When happens if you try to invoke the same WebHook with POST from Postman or CURL? If it works, I think you should look at the Dropbox side.

Yes, I'm using Lambda function URL, and it only works for the initial validation. Then, I modified some file to trigger the notifications, but it didn't work. I have similar code in CloudFunctions and it received the notifications. I reviewed in CloudWatch but there is nothing.