How do I fix AWS Lambda HEC error when parsing?

[lavster]

I wonder if someone can help, we are getting the following error when trying to send data into Splunk, this previously worked but now we cant seem to get it working at all,  I have tried to curl the event manually and it succeeds, which is even stranger. The error message is

token name=xxxx, channel=********* source_IP=******, reply=6, events_processed=0, http_input_body_size=101493, parsing_err="While expecting event object to start: Unexpected character while looking for value: 'E', totalRequestSize=101493"

the event we are trying to send looks like this

{
    "time": 1663679182,
    "host": "test-sandbox",
    "source": "aws/lambda",
    "sourcetype": "aws:lambda",
    "index": "xxx-xxx",
    "event": {
        "message": "2022/09/20 14:06:22 node=test-sandbox Starting to move cantabm_testfile-9.zip from c21-metadata-dropzone-sandbox to c21-metadata-dest-sandbox/Metadata/cantabm_testfile-9.zip\n",
        "account": "11111111111"
    }
}