---
"@context": https://schema.org
"@type": TechArticle
"@id": https://www.twilio.com/docs/api/errors/80604#article
headline: "80604: Proxy Identifier In Use"
url: https://www.twilio.com/docs/api/errors/80604
inLanguage: en
dateModified: 2026-06-08T12:04:59.000Z
author:
  "@type": Organization
  name: Twilio Developer Education Team
publisher:
  "@type": Organization
  name: Twilio
---

# 80604: Proxy Identifier In Use

Log Level: WARNING

## Description

Twilio returns this warning when the requested `proxyIdentifier` is already associated with the requested participant `identifier` in a way that would create a conflicting active mapping. In Proxy, the `identifier` and `proxyIdentifier` pair is used to route calls and messages, so reusing the same pair across active Sessions can cause traffic to be routed to the wrong recipient.

### Possible causes

* You tried to re-open a closed Session, and one or both Participants already have the same `identifier` and `proxyIdentifier` pair active in another Session.
* You supplied a specific `proxyIdentifier` or `proxyIdentifierSid` for a Participant, and that Proxy number is already in use for the same participant in another active Session.
* The same participant is active in concurrent Sessions, but the Service does not have enough Proxy numbers available to assign a different Proxy number for each active mapping.
* Your application is creating or re-opening Sessions close together in time, which can lead to duplicate active `identifier` and `proxyIdentifier` pairs if conflict handling is not enabled.

### Possible solutions

* Re-open a Session only when you know the affected Participants are not already active elsewhere with the same `proxyIdentifier`.
* If the same person must participate in concurrent Sessions, add more Twilio numbers to the Service so Proxy can assign a different number to each active mapping. A single participant cannot use the same Proxy number in concurrent active Sessions.
* Let Proxy select a number from the pool, or provide a different `proxyIdentifier` or `proxyIdentifierSid` that has already been added to the Service.
* Send `FailOnParticipantConflict=true` on Session create, Session update, and Participant create requests so Proxy rejects conflicting requests before they create ambiguous routing.
* If your account still allows participant conflicts, ask to remove the `ProxyAllowParticipantConflict` flag after you are ready to handle conflict responses on Session update and Participant create requests.

#### Additional resources

* [Participant resource](/docs/proxy/api/participant)
* [Session resource](/docs/proxy/api/session)
* [How many Phone Numbers do I need?](/docs/proxy/phone-numbers-needed)