What is partnerReferenceId in Web service APIs?

Hi all,
I have published a channel on Roku channel store.
In that I want to implement “cancel Subscription” of user from our end.
I want to use “//apipub.roku.com/listen/transaction-service.svc/cancel-subscription” i.e Cancel Subscription from Web Service API.[/font]
In above APIs request I have to send the following parameters:-
RokuAPIKey, TransactionID(Found after purchasing), CancellationDate, PartnerReferenceID(is it optional)

What is this PartnerReferenceID and how to get this partnerReferenceID ?

Thanks,
Ankit

I sent the same question to the Roku Support, but I have not received a reply yet.

The partner reference ID can be any value you set on your own server for the customer transaction. It is for your benefit, and optional.