# E12000 — SMSBackendUnavailable

The SMS service is temporarily unavailable. Please retry.

- **HTTP status**: `503`
- **Type**: `service_unavailable_error`
- **Name**: `SMSBackendUnavailable`

## What to do

This is a transient error and needs no change to your request. Wait a few seconds and send again; if it persists, retry with exponential backoff.

## Related

- [E12xxx — SMS sending & delivery](/docs/api/errors/E12xxx): every code in this range
- [Errors](/docs/api/errors): the full wire contract, status mapping, and error catalog
- [Error handling](/docs/guides/errors): branching on `type` and `code`, validation details, and `vendor_code`