When payment transaction data is sent to a payment provider by the Generic Payment webhook, the provider processes the payment information and returns information about the transaction. The webhook sends out a predefined set of properties in the request, and expects to receive another predefined set of properties back in the response. For some providers, however, you may need to send additional data in the request, and the provider may include additional data in the response. This section describes how you can send and receive additional data that is not included in the predefined properties.