---
"@context": https://schema.org
"@type": TechArticle
"@id": https://www.twilio.com/docs/api/errors/80409#article
headline: "80409: Session Sid Invalid"
url: https://www.twilio.com/docs/api/errors/80409
inLanguage: en
dateModified: 2026-06-08T12:04:59.000Z
author:
  "@type": Organization
  name: Twilio Developer Education Team
publisher:
  "@type": Organization
  name: Twilio
---

# 80409: Session Sid Invalid

Log Level: WARNING

## Description

You provided an invalid Proxy Session SID. Use a valid Session SID when you fetch, update, delete, or nest requests under a Proxy Session. A Proxy Session SID identifies a Session resource and uses the `KC` prefix with 32 hexadecimal characters.

### Possible causes

* The Session SID value does not match the required `KC` SID format or length for a Proxy Session resource.
* You used a different resource SID where a Session SID is required, such as a Service SID with the `KS` prefix or a Participant SID with the `KP` prefix.
* The `sid` or `SessionSid` request parameter for a Proxy endpoint was populated with a value that does not identify a Session resource.
* The Session SID was copied, stored, or passed incorrectly in your application and no longer matches the required Session SID pattern.

### Possible solutions

* Use the `sid` returned when you create or fetch the Proxy Session. A valid Session SID begins with `KC`.
* Validate the Session SID in your application before sending the request. Ensure it matches `^KC[0-9a-fA-F]{32}$`.
* Keep the Service SID and Session SID in the correct path parameters. Use the Service SID for `/Services/{ServiceSid}` and the Session SID for `/Sessions/{Sid}` or `/Sessions/{SessionSid}`.
* If you are calling a Participant endpoint, pass the Session SID in `SessionSid` and the Participant SID in `Sid`. Do not swap those values.

#### Additional resources

* [Proxy Session resource](/docs/proxy/api/session)
* [Proxy Participant resource](/docs/proxy/api/participant)
* [Proxy quickstart](/docs/proxy/quickstart)