The plugin provides a repository type named s3 which may be used when creating a repository. The repository defaults to using ECS IAM Role or EC2 IAM Role credentials for authentication. The only mandatory setting is the bucket name:

PUT _snapshot/my_s3_repository
{
  "type": "s3",
  "settings": {
    "bucket": "my-bucket"
  }
}

bucket: The name of the bucket to be used for snapshots. (Mandatory) Note that the bucket name can be between 3 and 63 characters long, and can contain only lower-case characters, numbers, periods, and dashes it cannot contain underscores, end with a dash, have consecutive periods, or use dashes adjacent to periods

The bucket naming convention is outlines in AWS here [https://docs.aws.amazon.com/awscloudtrail/latest/userguide/cloudtrail-s3-bucket-naming-requirements.html]