Vapi is the Voice AI platform for developers.

Vapi AI

**To fix the error, remove any `languageCode` property from your fallback voice configuration.** If you need to specify language, use `language` (not `languageCode`)—and only for providers that support it.

Example:
```json
{
  "voice": {
    "provider": "openai",
    "voiceId": "shimmer",
    "fallbackPlan": {
      "voices": [
        {
          "provider": "cartesia",
          "voiceId": "248be419-c632-4f23-adf1-5324ed7dbf1d",
          "language": "en" // Use "language" if needed, not "languageCode"
        }
      ]
    }
  }
}
```
Try this update and your assistant should publish without the error. For more details, see the [Voice fallback configuration documentation](https://docs.vapi.ai/voice-fallback-plan).

Source:
- [Voice fallback configuration documentation](https://docs.vapi.ai/voice-fallback-plan)

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