[SalesForce] ExactTarget (Marketing Cloud) Get Message Rest API call returning 500

I am attempting to retrieve all messages from our ExactTarget instance for an ETL. I am following the documentation from ExactTarget's code@ site. However the calls are returning a 500 Internal Server Error. Here is my request in Ruby:

  begin
    response = RestClient::Request.execute(:method => :get, :url => 'https://www.exacttargetapis.com/push/v1/message', :headers => {'Authorization' => 'Bearer ' + access_token}, :timeout => 600, :open_timeout => 600)
  rescue => e
    e.response
  end

This is the 500 error response:

{
  "documentation"=>"https://code.docs.exacttarget.com/rest/errors/500",
  "errorcode"=>0,
  "message"=>"Internal Server Error"
}

Note: the documentation link is dead.

The credentials used are good and using foo credentials results in a 401 Unauthorized response as expected. Is there a better way to extract all data from ExactTarget for an ETL system? Is it possible to get useful error codes from ExactTarget?