See also the Customer response object.

If you want to look up a single customer using its ID, use the find method.

Ruby 
customer = gateway.customer.find("a_customer_id")
This code snippet now uses gateway instance methods instead of class-level methods. Learn more.

If the customer can't be found, it will raise a Braintree::NotFoundError.

Arguments
customer_id required, String

A string value representing an existing customer in your Vault.