---
"@context": https://schema.org
"@type": TechArticle
"@id": https://www.twilio.com/docs/api/errors/13218#article
headline: "13218: Dial: Invalid sequential value"
url: https://www.twilio.com/docs/api/errors/13218
inLanguage: en
dateModified: 2026-03-11T18:38:39.000Z
author:
  "@type": Organization
  name: Twilio Developer Education Team
publisher:
  "@type": Organization
  name: Twilio
---

# 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)