demonstrating heroku exception when calling install_addon

heroku-install-addon.rb

require 'rubygems'
require 'heroku'

USERNAME = ''
PASS     = ''
APPNAME  = ''
ADDON    = 'pgbackups'

h = Heroku::Client.new(USERNAME, PASS)
h.install_addon(APPNAME, ADDON)

# results in...
# RestClient::UnprocessableEntity: 422 Unprocessable Entity
# 	from /Users/eignerchris/.rvm/gems/ruby-1.8.7-head/gems/rest-client-1.6.1/lib/restclient/abstract_response.rb:48:in `return!'
# 	from /Users/eignerchris/.rvm/gems/ruby-1.8.7-head/gems/rest-client-1.6.1/lib/restclient/request.rb:220:in `process_result'
# 	from /Users/eignerchris/.rvm/gems/ruby-1.8.7-head/gems/rest-client-1.6.1/lib/restclient/request.rb:169:in `transmit'
# 	from /Users/eignerchris/.rvm/rubies/ruby-1.8.7-head/lib/ruby/1.8/net/http.rb:543:in `start'
# 	from /Users/eignerchris/.rvm/gems/ruby-1.8.7-head/gems/rest-client-1.6.1/lib/restclient/request.rb:166:in `transmit'
# 	from /Users/eignerchris/.rvm/gems/ruby-1.8.7-head/gems/rest-client-1.6.1/lib/restclient/request.rb:60:in `execute'
# 	from /Users/eignerchris/.rvm/gems/ruby-1.8.7-head/gems/rest-client-1.6.1/lib/restclient/request.rb:31:in `execute'
# 	from /Users/eignerchris/.rvm/gems/ruby-1.8.7-head/gems/rest-client-1.6.1/lib/restclient/resource.rb:63:in `post'
# 	from /Users/eignerchris/.rvm/gems/ruby-1.8.7-head/gems/heroku-2.0.4/lib/heroku/client.rb:544:in `send'
# 	from /Users/eignerchris/.rvm/gems/ruby-1.8.7-head/gems/heroku-2.0.4/lib/heroku/client.rb:544:in `process'
# 	from /Users/eignerchris/.rvm/gems/ruby-1.8.7-head/gems/heroku-2.0.4/lib/heroku/client.rb:530:in `post'
# 	from /Users/eignerchris/.rvm/gems/ruby-1.8.7-head/gems/heroku-2.0.4/lib/heroku/client.rb:635:in `update_addon'
# 	from /Users/eignerchris/.rvm/gems/ruby-1.8.7-head/gems/heroku-2.0.4/lib/heroku/client.rb:618:in `configure_addon'
# 	from /Users/eignerchris/.rvm/gems/ruby-1.8.7-head/gems/heroku-2.0.4/lib/heroku/client.rb:492:in `install_addon'
# 	from (irb):12