How can we pass a custom field at Subscription Usage Event Level and send it to AR

Summary:

We have a requirement to pass a custom field used by the customer field while creating the subscription usage event object.

After that information to be passed to AR but usage event entity is not available in service mapping to map out of the box.

Content (please ensure you mask any confidential information):

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

26C

Code Snippet (add any code snippets that support your topic, if applicable):