Collaboration messaging framework XML customization - need xsd name

Summary: Need Collaboration messaging framework customization XSD name

Content (please ensure you mask any confidential information): We are building an integration to receive AR Outbound payload from CMK and process it. For this, we need the definition of ar/invoice element of the extension that Oracle sends when a custom logic is written via the "Load Extension Attributes for XML Transactions" Data Model in BI

<ar:Invoice xmlns:ar="http://www.oracle.com/ar/invoice">

Tried searching but not able to locate the definition.

Version (include the version you are using, if applicable):

<ns1v2:MessageDefinition>
<ns1v2:DocumentType xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="">Invoice</ns1v2:DocumentType>