       if response['ACK'] is 'Failure'
         callback response['L_LONGMESSAGE0']
       else
-        callback null, response
+        callback err, response
 
   # Modifies the state of an existing subscription by invoking the
   # ManageRecurringPaymentsProfileStatus on the PayPal API.

      if response['ACK'] is 'Failure'
        callback response['L_LONGMESSAGE0']
      else
        callback null, response

  # Returns subscription information for an already created subscription by
  # invoking the "GetRecurringPaymentsProfileDetails" method in the PayPal API.

      if response['ACK'] is 'Failure'
        callback response['L_LONGMESSAGE0']
      else
        callback err, response

  # Performs the actual API request to the PayPal API endpoint.
  #
