AWS stepfunctions - passing and reading variables from lambda function - json

Question

I am trying to read output from my lambda function into a variable in my step function. The lambdas default output is
return {
'statusCode': 200,
'body': json.dumps('Hello from Lambda!')
}
What I would like to return is a json object like this
{
"version": version,
"bucket": bucket
}
where the version and bucket name gets passed from the lambda. in my step function, I am trying to capture this and insert it into an s3 url like this:
"S3Uri.$": "States.Format('s3://{}/path/to/script/{}/script.py',$.bucket, $.version)"
However, I am struggling with having the correct output from the lambda and how to grab the value in step functions. I've tried
return {
'statusCode': 200,
'body': json.dumps({
"version": version,
"bucket": bucket
}) }
And various ways of constructing the json object as a string to the body, eg
"{\"version\": \"" + version + "\",\"bucket\": \"" + bucket + "\"}"
But I can't find the right combo, and the job keeps failing. Here is an example error message
The JsonPath argument for the field '$.bucket' could not be found in
the input '{"statusCode": 200, "body": "{\"version\":
\"v0-1\", \"bucket\":
\"sagemaker-us-west-2-removed\"}"}'"
How should I construct the lambda output, and the corresponding step function variable to have the values pass through? Again, I want the lambda to tell step functions what bucket and version was used, and then have step functions insert these values into an s3 url string.
EDIT: here is the full error message for one of the attempts
{
"error": "States.Runtime",
"cause": "An error occurred while executing the state 'Postproc' (entered at the event id #38). The function 'States.Format('s3://{}/AAPM/AAPM_2207/prod/{}/meta/scripts/preproc/aapm-postproc.py',$.bucket, $.version)' had the following error: The JsonPath argument for the field '$.bucket' could not be found in the input '{\"statusCode\": 200, \"body\": \"{\\\"version\\\": \\\"v0-1\\\", \\\"bucket\\\": \\\"sagemaker-us-west-2-removed\\\"}\"}'"
}

Answer 1

As in this answer the trick was just to get rid of json dumps.
return {
'statusCode': 200,
'body': {
"version": version,
"bucket": bucket
}
}
and I could access them fine with $.bucket, $.version