New Test Mode — login screen unresponsive; CORS failure on sandbox /sync endpoint (legacy Test Mode works)

[m-corderoy]

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• I give permission for members of the FlutterFlow team to access and test my project for the sole purpose of investigating this issue.

Current Behavior

Possibly related to #7159 ("Test Mode – Broken for a few days – CORS"), but filing separately because I have a clean new-vs-legacy Test Mode repro and console logs that may help move that one past "can't reproduce."

With "Use new Test Mode" enabled, the app loads to the login screen but the screen is unresponsive — tapping the login button does nothing and no authentication is attempted. The browser console shows a CORS failure on FlutterFlow's own sandbox sync endpoint, followed by ERR_FAILED:

Access to fetch at 'https://sandbox-ygxkweukma-uc.a.run.app/api/sandboxes/<id>/sync'
from origin 'https://app.flutterflow.io' has been blocked by CORS policy:
No 'Access-Control-Allow-Origin' header is present on the requested resource.
sandbox-...:/sync:1  Failed to load resource: net::ERR_FAILED

Expected Behavior

Ability to login via firebase auth

Steps to Reproduce

1. Open the project in Test Mode with "Use new Test Mode" enabled.
2. Let the app load to the login screen.
3. Attempt to log in (Firebase Auth , via email/password).
4. Observe: the button does nothing, no auth is attempted, and the console shows the CORS/ERR_FAILED on …/api/sandboxes//sync.
5. Disable "Use new Test Mode" and repeat → works normally.

Reproducible from Blank

• The steps to reproduce above start from a blank project.

Bug Report Code (Required)

ITFXkMmA8Yt2rsBE0bXcY+5GiiYwFjMMbY0v0u0bFB4jIZOqEKQlP/T8S0NKTfW7fFVqDGf8oHkxpK3vufPfKcE6PUyCb7pH0JVAchbMRj+ib7KuPbqOVXFAO/NQJ2qx3Img3RN4ItRfWXAT21+bNq3qNleeY8aSfxBlZ7vfcPo=

Visual documentation

n/a

Environment

- FlutterFlow version: 7.0.6 (released 4 June 2026)
- Flutter version: 3.38.5
- Platform: Web (Test Mode)
- Browser name and version: Chrome Version 148.0.7778.217 (Official Build) (arm64)
- Operating system: macOS Tahoe 26.5
- Auth: Firebase Auth + Supabase (using minted token)

Additional Information

Toggling new vs legacy Test Mode is a reliable on/off switch for the bug

[Alezanello]

Thank you for reporting this issue. I've shared it with our engineering team for further investigation and a fix.