Serverless-s3-sync TypeError: Cannot read property 'length' of undefined

Serverless Framework
1

Hello,

I’m trying to copy a yaml file to an S3 bucket.
but each time sls gives me an error :
TypeError: Unable to read the ‘length’ property of undefined.

do you know what it is please ?

here is the package.json.

{
“name” : “jsonfiles”,
“version” : “1.0.0”,
“description” : “”,
“dependencies” : {},
“devDependencies” : {
“serverless-plugin-log-retention”: “^2.0.0”,
“serverless-python-requirements”: “^5.1.0”,
“serverless-s3-sync” : “^1.17.1”
},
“author”: “Matthieuk”,
“license” : “ISC”
}

and the s3Sync section:
s3Sync:
- bucketName : hosting-prod
bucketPrefix : jsonfiles/
localDir : json

thanks a lot.