Custom GPT Actions work in text but never execute in Voice Mode (InvalidRecipient : Unrecognized recipient))

Hi,

I’m trying to determine whether this is a known limitation or a bug.

I created a minimal Custom GPT with a single GET Action using the following OpenAPI:

openapi: 3.1.0
info:
  title: Test Voice API
  version: 1.0.0
servers:
  - url: https://httpbin.org
paths:
  /get:
    get:
      operationId: testGet
      responses:
        "200":
          description: OK

GPT instructions:

Whenever the user says “test”, always call the action testGet.

Results

Text mode

• Works correctly.

• The Action executes and the HTTP request reaches httpbin.

Advanced Voice Mode (Android app and ChatGPT Web using a microphone)

• The Action is never executed.

• The assistant reports a technical issue.

• No HTTP request reaches the server.

Additional observation:

If I type “continue” immediately after the failed voice interaction, ChatGPT is sometimes able to inspect its previous attempt and reports that it encountered:

InvalidRecipient Unrecognized recipient: httpbin_org__jit_plugin

This suggests the failure may occur before any HTTP request is sent.

I first observed this with my own FastAPI backend, then reproduced it with the public httpbin.org endpoint, so it doesn’t appear to be API-specific.

Has anyone successfully executed Custom GPT Actions from Advanced Voice Mode recently?

If yes:

• Android / iOS / Web?

• Which model?

• Any specific configuration?

Thanks!