# TARGETING_KEY_MISMATCH

- Surface: API
- HTTP status: 409
- Recommended action: `CREATE_NEW_RUN`
- Details: `{ currentTargetingKey: string, attemptedTargetingKey: string, experimentId: string, recommendedAction: RecommendedAction }`

## Cause

The Targeting Key changed on a Run that is already assigning traffic. Every Entity would rebucket, and the Exposures already recorded would describe a different population than the ones that follow.

## Fix

Start a new Run with the new Targeting Key. The old Run keeps its measured cohort intact; the new one buckets from scratch.

## Related

- [RUN_FROZEN](https://splitch.dev/docs/error/RUN_FROZEN)
- [MULTIPLE_VARIANT_CONFLICT](https://splitch.dev/docs/error/MULTIPLE_VARIANT_CONFLICT)

Source: https://splitch.dev/docs/error/TARGETING_KEY_MISMATCH