---
"@context": https://schema.org
"@type": TechArticle
"@id": https://www.twilio.com/docs/api/errors/82009#article
headline: "82009: Multi-valued headers not supported"
url: https://www.twilio.com/docs/api/errors/82009
inLanguage: en
dateModified: 2026-03-11T22:03:37.000Z
author:
  "@type": Organization
  name: Twilio Developer Education Team
publisher:
  "@type": Organization
  name: Twilio
---

# 82009: Multi-valued headers not supported

Log Type: APPLICATION

Log Level: ERROR

## Description

Twilio was unable to process the correct response to your Function invocation because your version of Functions is incompatible with multi-valued HTTP response headers.

### Possible causes

A Function invocation has resulted in a Twilio Response with multi-valued headers (i.e. the header value is an array). Multi-valued headers are not supported in Classic Functions, or in @twilio/runtime-handler dependency versions below 1.2.0.

### Possible solutions

Use the new Functions/Assets UI or Serverless API, and upgrade your @twilio/runtime-handler dependency version to 1.2.0 or higher. Please refer to [this](/docs/serverless/functions-assets/handler) for more information about the Runtime Handler, how to upgrade the version, and the currently available versions. For Classic Functions, or incompatible Runtime Handler versions, only String-valued headers are permitted.