anchor.diff:  
   The plugin will deserialize either the request body and/or the url query parameters to process the notification and return a properly formatted HTTP response object for the gateway (some gateways require specific reponse codes or headers to consider the notification processed and prevent retries).
   
  +Because this endpoint needs to be on a public IP (to be accessible from the gateway), we recommend using the https://github.com/killbill/killbill-notifications-proxy[Kill Bill Notifications Proxy] to avoid exposing the entire Kill Bill server.
  +
   === Examples of hosted pages flows
   
   The implementation of the *buildFormDescriptor* and *processNotification* APIs described above will vary from gateway to gateway. Here are a couple of example flows.
  +
  +While the internal mechanics of completing the payment vary for each plugin, the overall steps are usually the same:
  +
  +. Your website calls *buildFormDescriptor* and interprets the result
  +. The customer is then either shown a payment form or redirected to an external page
  +. The customer completes the payment
   
   ==== Gateway notifies Kill Bill of the payment
   
  
positive.code: 
  Notes:
  
  * You can specify another payment method (other than the default one) via the *paymentMethodId* query parameter
  
  [[gateway-notification]]
  
negative.code: 
  The *buildFormDescriptor* call is used when you need to prepare a payment form. There are two main scenarii:
  
  * The payment form is hosted on your own website. The exact fields to add in this form are returned by the plugin. These can be:
  ** required visible fields, such as the amount of the payment. The plugin will return the name expected by the gateway (e.g. *Sum* instead of *amount*)
  ** hidden fields (e.g. *merchantId* value)
  * The payment form is hosted on the gateway website. In that case, the plugin builds a unique URL to redirect the user to by either:
  ** submitting the order information (amount, etc.) to the gateway which returns the location of the hosted payment form
  ** constructing the special URL via query parameters
  