For the case of this header, you're interacting with third parties that don't speak your application domain. That "unique id" you mention is exactly the use ca

For the case of this header, you're interacting with third parties that don't speak your application domain. That "unique id" you mention is exactly the use case for the idempotency key this RFC proposes. You can model your unique basket identifier in your application domain, and use that identifier as the idempotency key in interactions with third parties. This is useful mostly because networks and applications are not necessarily reliable.