Antigravity login and Handshake Failure and Incorrect GCH Project ID Prompt

Google Antigravity
1

​I am reporting a persistent authentication failure with the Google Antigravity desktop application.
​The Problem:
I successfully authenticate via the browser and reach the confirmation page. However, the desktop application does not receive the handshake signal. After multiple attempts, the app incorrectly prompts me to enter a Google Cloud Project ID, which is not applicable to my account.
​Troubleshooting Performed:
I have successfully authenticated in both Chrome and Microsoft Edge. I have completely disabled Windows Firewall across Domain, Private, and Public profiles. I have also cleared the local application cache and session data in AppData and restarted the system.
​The browser confirms OAuth Success, but the app remains stuck or defaults to the GCH login screen. This appears to be a backend provisioning issue or a failure in the local protocol handler.

OS: Windows

4

I had same prolem.

Here is a complete, ready-to-share markdown post you can drop into GitHub, Reddit, or a community forum to help anyone else hitting this wall.

Gemini 3.5 flash solved this while 3.1 pro was doing the laps around… anyway i fixed with that.

[FIX] Google Antigravity Windows Handshake Failure / Loopback OAuth Error

If you are trying to set up the Google Antigravity desktop client on Windows and getting stuck on the Google account login—or if it constantly throws fake “admin restrictions” or “billing account invalid” errors—the app is failing its internal OAuth handshake.

Why this happens

The desktop client uses an internal networking library called gaxios. When the browser redirects back to your computer after a successful Google login, gaxios strictly enforces a TLS check on the local loopback callback (localhost). Because the local callback isn’t running on a signed SSL certificate, the handshake fails silently, drops your authentication token, and defaults to throwing generic billing/admin errors.

Here is how to manually patch the file and bypass the broken handshake.

Step-by-Step Solution

1. Close Antigravity Completely

Make sure the Antigravity desktop app is fully closed and not lingering in your Windows system tray or background processes.

2. Open the Target Folder

Instead of hunting through hidden folders, press Win + R to open the Run dialog box, copy and paste the following path, and hit Enter:

Plaintext

%LocalAppData%\Programs\Antigravity\resources\app\node_modules\gaxios\build\cjs\src\

(Note: If you installed the app globally rather than just for your user profile, the path will be under C:\Program Files\Antigravity\... instead. You can find it by right-clicking the app icon and selecting Open file location).

3. Patch gaxios.js

  1. Look for a file named gaxios.js, right-click it, and open it with a text editor (Notepad, VS Code, etc.).

  2. Near the very top of the file, locate this line:

    JavaScript

    const https_1 = require("https");

  3. Immediately below it, paste this line to force Node to accept the local authentication redirect:

JavaScript

   process.env.NODE_TLS_REJECT_UNAUTHORIZED = "0";
  1. Save the file and close the editor.

4. Relaunch and Authenticate

Fire the Antigravity app back up and click Sign in with Google. Your browser will handle the login, and the desktop client will now successfully catch the loopback handshake without crashing.