# 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.