Add your AWS authentication credentials to config/config.exs
:
config :amazon_product_advertising_client,
associate_tag: "YourAssociateTag",
aws_access_key_id: "YourAccessKeyID",
aws_secret_access_key: "YourSecretAccessKey",
marketplace_host: "webservices.amazon.ca" # If not specified the default value is webservices.amazon.com