Historically, we’ve allowed you to optionally specify a custom ID for each passenger when creating an offer request. These custom IDs are then used throughout the API.
We recently marked this feature as deprecated, and we’ve now removed it from our documentation. If you’re currently specifying custom passenger IDs, this will continue to work, and you do not need to make any changes to your integration.
We plan to drop support for this feature in the API at some point in the future. Before we do, we’ll give you plenty of notice and will offer you support with the change (including a migration guide).