# What does the VARTA error `session_not_found` mean?

The session (or call) id you supplied is not a value this API ever issued.


**HTTP status:** `404`  ·  **Type:** `invalid_request_error`

## What it means

The session (or call) id you supplied is not a value this API ever issued.

## What causes it

Raised when a session or call id fails to decode (`backend/app/api/v1/_ids.py`), from the `/v1/sessions/{session_id}...` endpoints (`backend/app/api/v1/sessions.py`) and from `GET /v1/calls/{call_id}` (`backend/app/api/v1/calls.py`). That last case is worth noting specifically: call lookups are keyed by the underlying session, so a malformed `call_id` reports as a missing session, not a missing call.

## What to do

Check the id is one this API returned. If you're calling `GET /v1/calls/{call_id}` and see this code, the `call_id` itself is malformed — it isn't a signal that the call doesn't exist.