Fix · Sign-in and accounts

Google sign-in error: redirect_uri_mismatch

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What you may see

The Google sign-in page shows error 400 and redirect_uri_mismatch
Sign in with Google works on localhost, not on the live site

Most likely cause

The address that Google sends the person back to must be in the allowed list in the Google project, and exactly as the app uses it (https, domain, path).

Check first (about two minutes)

The error page shows the address the app sent: copy it (it is not a secret).
Open the sign-in settings in the Google project and compare the allowed addresses.

The fix prompt

What you type here never leaves your browser. The search runs on this page, and nothing is sent to a server or to an AI.

The exact error or what you see

What you did before it happened

Kept only in this browser, on this device. Keys and passwords are removed before anything is saved.

Prompt language

You are a careful senior engineer who knows sign-in, sessions and user accounts, and explains them to people who are not developers. I am not a developer, so explain every step in plain words and tell me exactly which button, menu or command you mean. If you are not sure about something, say so; do not guess.

Menu and button names change over time. If you cannot find a button or page I mention, say so and tell me what to look for instead of guessing.

THE PROBLEM
Google sign-in error: redirect_uri_mismatch

THE EXACT ERROR OR WHAT I SEE
[paste the exact error here]

WHAT I DID BEFORE IT HAPPENED
[write in a few words what you did before it happened]

MOST LIKELY CAUSE
The address that Google sends the person back to must be in the allowed list in the Google project, and exactly as the app uses it (https, domain, path).

DO THESE STEPS, IN THIS ORDER
1. Ask me for the exact address shown in the error and the list of allowed addresses I have.
2. Tell me the exact addresses to add for the live site, the www version if used, and localhost for development; also the callback address of my sign-in service if one is used (for example the auth service of my database).
3. Check the app uses the live site address from one setting, not a fixed local one.
Stop and tell me if what you see does not match a step. Do not skip ahead.

CHECK THAT IT WORKED
- A test Google sign-in on the live site returns to the app logged in, with no 400 page.
Tell me exactly what I should see on the screen when it works.

DO NOT CHANGE
- Do not add a wildcard or unrelated addresses.
- Anything I did not ask about: the design, the text, other pages, other settings or the data.
- Do not delete files, data or branches, do not reset or force-push, and do not rewrite history, unless you first show me exactly what would be lost and I say yes.
- Do not paste, print or ask me to paste a password or secret key into this chat. If one is needed, tell me which settings page of the right service to store it in.

WHEN YOU FINISH
Explain in simple words what you changed (file by file or setting by setting), why you changed it, and how I can undo it.

Paste it into Claude, ChatGPT, Gemini or Cursor, then follow what it says.

After you tried it, did it work?

Steps

Ask me for the exact address shown in the error and the list of allowed addresses I have.
Tell me the exact addresses to add for the live site, the www version if used, and localhost for development; also the callback address of my sign-in service if one is used (for example the auth service of my database).
Check the app uses the live site address from one setting, not a fixed local one.

Do not do this

Do not share the client secret in chat.
Do not add a wildcard or unrelated addresses.

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