# 13218: Dial: Invalid sequential value

Log Type: APPLICATION

Log Level: WARNING

## Description

The `sequential` attribute on `<Dial>` only accepts `true` or `false`. Setting `sequential="true"` lets Twilio call up to ten agents one after the other, in the order they are specified in the verb.

### Possible causes

The `sequential` attribute on `<Dial>` was set to a value other than `true` or `false`.

### Possible solutions

* Update the `<Dial>` verb so `sequential` is set to either `true` or `false`.
* If you need sequential dialing, set `sequential="true"` on `<Dial>` so Twilio calls up to ten agents one after the other in the specified order.

#### Additional resources

* [TwiML Voice: `<Dial>`](/docs/voice/twiml/dial)
* [Error and Warning Dictionary](/docs/api/errors)