How to save a default file to S3 bucket at sign up via controller method?

At signup of a new user, I would like my Rails application to automatically copy a standard file for that user to my S3 bucket.

How can I use the aws-s3 gem/aws-sdk gem and how can I store the path to where the file is saved in the S3 bucket in my Drawing model?

gem 'aws-sdk', '~> 2'

I have added this instead of gem aws-s3 to my gemfile. Aws-s3 seems a bit old and I understand that aws-sdk is the main gem of Amazon Aws and includes the s3 gem?

Next, following this relevant post, I added to the organizations controller the method upload_file:

def create
  @organization = Organization.new(organizationnew_params)
  if @organization.save
    upload_file(@organization.id)
    redirect_to root_url
  end
end

private
def upload_file(id)
  s3 = Aws::S3::Resource.new(
       credentials: Aws::Credentials.new(ENV['S3_ACCESS_KEY'], ENV['S3_SECRET_KEY']),       # These environmental variables I had already set for the uploader I have previously created.
       region: ENV['AWS_REGION']
       )
  xmlfile = 'other/graph.xml'           # Correct path? This file is located in app/assets/other/graph.xml
  directory = "graphs/#{model.class.to_s.underscore}/#{mounted_as}/#{id}"
  s3.bucket('mybucketname').object(ENV['S3_ACCESS_KEY']).upload_file(xmlfile)
end

Error message: This current setup generates the error below (referring to the line s3 = Aws::S3::Resource.new). I've of course double checked that I've set heroku config:set AWS_REGION=eu-west-1, which I did. I don't understand the cause of the error.

missing region; use :region option or export region name to ENV['AWS_REGION']

Additional issues:

• I would like to give the file a custom name: "graph#{id)". How to specify this?
• I would like the method to save to the directory in the S3 bucket that I specified in the private method. How to do this?
• I established a 1:1 relationship between the model Drawing and the model Organization. Drawing contains 2 variables: organization_id and file_path. File_path should include the string to the file that we will save to the S3 bucket at signup. How to create the association between file_path in the Drawing model and the uploaded file in the S3 bucket?