Cloudwatch to Firehose problem

Hello!,

Im facing some issue while trying to stream data from cloudwatch to opensearch using firehose as middleware, the message that is giving me Opensearch, after running the transformation Lambda is:

Check your function and make sure the output is in required format. In addition to that, make sure the processed records contain valid result status of Dropped, Ok, or ProcessingFailed

but my lambda is returning correctly the expected structure for the transformation:

{'records': [{'recordId': '49636899004605693948429040836377972132019587527722663938000000', 'result': 'Ok', 'data': '...'}]}

Actually I'm using python for the transformation Lambda

 recordData = {
            'recordId': recordIdD,
            'result': 'Ok',
            'data': base64.b64encode(dataToSend).decode("utf8")
        }

Any advice about this issue to make the pipeline work?

Thanks in advance