Desktop app: "ChatGPT Plus/Pro" device authorization fails with 403 (Token exchange failed / Failed to initiate device authorization)

Description

Environment

Platform: macOS
App: OpenCode desktop app (app.asar bundled, @opencode-ai/plugin@local dependency install warning present)
Provider: built-in openai (ChatGPT Plus/Pro subscription, device/authorization-code flow)
Describe the bug When adding the OpenAI provider via ChatGPT Plus/Pro login, the device authorization flow fails repeatedly with 403:

Error: Token exchange failed: 403
Error: Failed to initiate device authorization
Both originate in exchangeCodeForTokens / ProviderAuth.authorize on the opencode auth server side. A DeepSeek API key stored alongside works fine, so it's specific to the OAuth/device flow.

Steps to reproduce

Open the desktop app → Settings → add OpenAI provider
Select ChatGPT Plus/Pro login
Observe 403 on device authorization / token exchange
Expected behavior The browser opens the OpenAI authorization page; after approving, the app exchanges the code for a token and the ChatGPT models become available.

Actual behavior Authorization is rejected with 403 before/at token exchange.

Logs

timestamp=... level=ERROR run=... message=failed ref=err_... error="Error: Token exchange failed: 403"
cause="Error: Token exchange failed: 403
at exchangeCodeForTokens (.../node-paSOqpta.js:398919:11)
at ProviderAuth.callback (.../node-paSOqpta.js:669764:39)
at Server.listen (.../node-paSOqpta.js:671710:52)"
timestamp=... level=ERROR run=... message=failed ref=err_... error="Error: Failed to initiate device authorization"
cause="Error: Failed to initiate device authorization
at Object.authorize (.../node-paSOqpta.js:399213:21)
at ProviderAuth.authorize (.../node-paSOqpta.js:669751:46)
at ProviderHttpApi.authorizeRaw (.../node-paSOqpta.js:385447:31)"
Notes

Region/network: user's IP may be outside regions supported for the OpenAI device flow (possible cause).
Secondary: desktop bundle emits repeated background dependency install failed ... @opencode-ai/plugin@local: No matching version found warnings — a packaging issue, seemingly unrelated, worth a separate look.
Would be helpful if the server returned a clearer error (e.g. region-not-supported, account-eligibility) instead of a bare 403.

opencode-debug-20260806T182010.zip

Plugins

No response

OpenCode version

mac 1.18.14 (1.18.14)

Steps to reproduce

No response

Screenshot and/or share link

Operating System

macos 14.8

Terminal

GUI