> For the complete documentation index, see [llms.txt](https://docs.tryterra.co/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.tryterra.co/faq/help-topics/data-api-sdk/authentication-users-and-connection-state/user-uniqueness-reference-id.md).

# Why are multiple user\_ids created for one reference\_id?

Each Terra `user_id` represents a **single user-provider connection**, and every data request is scoped to one `user_id` (one call returns one provider's data).

`reference_id` is purely metadata to help you reconcile users on your side. It carries no dedup logic, so `reference_id` + provider does not guarantee a unique record. A previous `user_id` is only replaced (via a reauth event) when the same provider account is authenticated again under the same developer ID.

Two active connections sharing a `reference_id` and provider but with different `user_id`s usually means the user connected from two different devices or accounts.

To combine providers for one end user:

* Make separate calls per `user_id`.
* Map them via the `reference_id` supplied at [authentication](https://docs.tryterra.co/health-and-fitness-api/user-authentication).

Filtering below the data-type level must be done in your own application logic.