TL;DR: TwilioRestClient died in twilio 6.0. Replace `from twilio.rest import TwilioRestClient` with `from twilio.rest import Client`, and TwilioRestClient(account_sid, auth_token) with Client(account_sid, auth_token).

```text
ImportError: cannot import name 'TwilioRestClient' from 'twilio.rest'
```

## Fix it

1. Change the import: from twilio.rest import Client. Expected: imports cleanly.
2. Change instantiation: client = Client([account sid], [auth token]). Expected: same object shape as before.
3. Update method calls if old: client.messages.create(...) works on both, but check the v6 changelog for renames you use. Expected: tests pass.
4. Pin twilio>=6 in requirements (or >=7/8 for current) so installs stay consistent.

## When this applies
- The code imports TwilioRestClient and twilio is 6+.

## When it doesn't
- twilio is 5.x: TwilioRestClient exists; reinstall if the import fails.
- The import works but API calls 401: credential problem, not this.

## Compatibility
- twilio >= 6.0. Current is 8.x/9.x.

## Why it happens
v6 unified the client classes and removed the legacy name. Old quickstart code copied from pre-2017 docs still shows TwilioRestClient.

## Edge cases
- TaskRouter and other sub-clients moved too; check imports for the full client surface you use.