elasticsearch snapshot to AWS s3 mock

for testing purpose I want to create elastic-search snapshot to S3 mock.

I use mock from https://www.npmjs.com/package/s3rver

I have repository-s3 6.2.2 plugin installed. When I try to register new snapshot:

PUT _snapshot/my_s3_repository
{
  "type": "s3",
  "settings": {
      "bucket": "rtbackup",
      "endpoint": "localhost:9495",
      "protocol": "http"
  }
}

I got "Unable to load credentials from service endpoint".

I would like to avoid of using any AWS services while testing. Any idea, how to force elastic to create snapshot in s3rver mock?