---
"@context": https://schema.org
"@type": TechArticle
"@id": https://www.twilio.com/docs/api/errors/13110#article
headline: "13110: Annotate: Annotate must contain one valid nested element"
url: https://www.twilio.com/docs/api/errors/13110
inLanguage: en
dateModified: 2026-06-09T11:00:42.000Z
author:
  "@type": Organization
  name: Twilio Developer Education Team
publisher:
  "@type": Organization
  name: Twilio
---

# 13110: Annotate: Annotate must contain one valid nested element

Log Level: ERROR

## Description

Twilio returns this error when you send Voice TwiML with an `<Annotate>` element that does not contain a valid child element. Twilio only allows `BillingReferenceTag` inside `<Annotate>`, so an empty `<Annotate>` element or one that contains a different child element triggers this error.

### Possible causes

* `<Annotate>` is empty and does not include a `BillingReferenceTag` child.
* `<Annotate>` contains a nested element other than `BillingReferenceTag`. Twilio only allows `BillingReferenceTag` inside `<Annotate>`.
* The nested element name is misspelled or uses the wrong case. TwiML element names are case-sensitive.

### Possible solutions

* Add a valid `BillingReferenceTag` child inside `<Annotate>`. For example, use `<Annotate><BillingReferenceTag>order-123</BillingReferenceTag></Annotate>`.
* Remove any unsupported child elements from `<Annotate>` and keep only `BillingReferenceTag`.
* Verify that the child element name and casing exactly match `BillingReferenceTag`.
* Keep the `BillingReferenceTag` value at 128 characters or fewer to avoid error 13120.

#### Additional resources

* [TwiML for Programmable Voice](/docs/voice/twiml)
* [Call Annotation Resource](/docs/voice/voice-insights/api/call/call-annotation-resource)
* [Debugging your Twilio application](/docs/usage/troubleshooting/debugging-your-application)