How do I process a new reference transaction using XMLPay?

The XMLPay Core Specification Guide's DTD and schema define the RepeatSale element, but PayPal currently doesn't support this functionality. However, you can apply the following workaround, which uses the ExtData field.

Disclaimer: PayPal doesn't support this code and provides it for demonstration purposes only. For more information, see the PayPal Developer Portal.
<?xml version="1.0" encoding="UTF-8"?>
<XMLPayRequest Timeout="30" version = "2.0" xmlns="">
<ExtData Name="ORIGID" Value="VXYZ12345678"></ExtData>