> For the complete documentation index, see [llms.txt](https://docs.digitalriver.com/digital-river-api/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.digitalriver.com/digital-river-api/integration-options/checkouts/creating-checkouts/providing-an-upstream-identifier.md).

# Providing an upstream identifier

The `upstreamId` can be any identifier you want to associate with a [checkout](https://docs.digitalriver.com/digital-river-api-reference/2021-12-13/checkouts), [order](https://docs.digitalriver.com/digital-river-api-reference/2021-12-13/orders), and [invoice](https://docs.digitalriver.com/digital-river-api-reference/2021-12-13/invoices). Unlike metadata, you can use this value as a query parameter in `GET` requests.

For tracking purposes, we recommend you provide the universally unique identifier (UUID) that clients use to identify the corresponding order in their system.