> ## Documentation Index
> Fetch the complete documentation index at: https://ngrok.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Error 438

## ERR\_NGROK\_438

Invalid '\_' in domain name. Valid domains may not contain underscores. Failed to reserve `DOMAIN`.

## Further help

If you're having trouble resolving this error, please reach out to [support@ngrok.com](mailto:support@ngrok.com?subject=Help%20with%20ERR_NGROK_438)