Review Diff always fails with "Oops, an error has occurred" (403 Forbidden)

[ngtrunghau]

What version of the IDE extension are you using?

26.721.41059

What subscription do you have?

ChatGPT Plus

Which IDE are you using?

Visual Studio Code

What platform is your computer?

No response

What issue are you seeing?

Summary

The ChatGPT Codex VS Code extension successfully edits files, but the Review/Diff UI always fails.

Instead of showing the generated diff, it displays:

Oops, an error has occurred

Sometimes the Codex Diff tab also shows:

No diff available

Environment

• VS Code: 1.130.0
• ChatGPT / Codex extension: 26.721.41059
• OS: Windows 11
• ChatGPT Plus
• Login method: Microsoft account

Steps to reproduce

1. Open a workspace.
2. Ask Codex to modify a file.
3. Wait until the changes are applied.
4. Click Review.

Expected behavior

The Review page should display the generated diff.

Actual behavior

The Review page always shows:

Oops, an error has occurred

The code changes are successfully applied to the files, but the diff cannot be viewed.

Logs

Developer Console shows:

• HTTP 403 Forbidden when requesting Codex backend endpoints.
• Error from fetching httpStatus=403
• Thread context is unavailable for non-thread routes

The changes are applied correctly, so the issue appears to affect only the Review/Diff UI.

Additional information

I have already tried:

• Reload Window
• Restart VS Code
• Sign out and sign back in

The issue persists.

What steps can reproduce the bug?

1. Open Visual Studio Code.
2. Open any workspace or project.
3. Open the ChatGPT Codex extension.
4. Ask Codex to modify an existing file.
5. Wait for the edit to finish. The code changes are successfully applied.
6. Click the "Review" button to view the generated diff.

Result:
The Review page shows "Oops, an error has occurred" instead of displaying the diff.

Additional information:
The modified code is correctly written to the file, but the Review/Diff view fails. The Developer Console shows HTTP 403 Forbidden errors when requesting the Codex backend.

What is the expected behavior?

No response

Additional information

No response

[github-actions]

Potential duplicates detected. Please review them and close your issue if it is a duplicate.

• [VS Code] Codex Diff editor tab always crashes with "Thread context is unavailable for non-thread routes" #35076
• Codex not showing diff #35156
• Codex Diff shows “Oops, an error has occurred” in VS Code #35481
• VS Code extension: full Review diff page crashes while inline diff works #35362
• Issues to open Codex Diff files. #35250

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