Keep getting Bad Request - Error 400

Question

Please help me resolve my issue as I can't log in to Outlook on my Desk Top computer as it keeps indicating Bad Request Error 400, Thank you.

Answer 1

Hi, I'm John! I will help you with this.

Have you already tried the suggestions from the error message?

You can find the link here: https://support.microsoft.com/account-billing/error-400-when-signing-in-7af27146-7624-4397-a374-6f8eae4367fe

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If issue still persists, just to check if the issue is specific to Outlook, could you try signing in to your Microsoft account at https://account.microsoft.com or https://outlook.live.com/mail and let me know if that works?

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Click "Add comment" to let me know.

Regards,

John J.D.

Answer 2

Error 400 in this scenario usually means the sign-in request with a password could not be processed, often due to too many attempts in a row or an issue with the app, browser, device, or network.

Try these steps in order:

1. Use a different sign-in method
   • At the Outlook/Microsoft account sign-in prompt on the desktop, select Other ways to sign in.
   • If available, choose one of these instead of the password:
     • Use face, fingerprint, PIN, or security key
     • Approve sign-in with the Microsoft Authenticator app
     • Send a code to email or phone
   • If codes do not arrive or fail, see the guidance in Troubleshoot Microsoft verification code issues.
2. Update or reinstall the Outlook/Microsoft app
   • If the error appears inside a Microsoft app on the desktop (for example, the Outlook app from Microsoft Store):
     • Uninstall the app.
     • Reinstall the latest version from the Microsoft Store.
     • Try signing in again.
3. Switch device
   • Try signing in to Outlook (for example via Outlook on the web or the Mail app) from another device such as a different PC, tablet, or phone.
   • If sign-in works elsewhere, the issue is likely specific to the original desktop (local app, profile, or browser cache).
4. Change network
   • If using Wi‑Fi, switch temporarily to a different network (for example, mobile hotspot) and try again.
   • If using mobile data, try a trusted Wi‑Fi network.
5. If still blocked after many attempts
   • If repeated attempts continue to fail and you cannot use any alternate sign-in method, wait at least 24 hours with no further sign-in attempts before trying again, as repeated failures can temporarily block password sign-in.

If none of these steps work and no alternate sign-in method is available, use the Microsoft account recovery and support options referenced from the Error 400 and verification-code troubleshooting pages.

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References:

• Error 400 when signing in
• Troubleshoot Microsoft verification code issues
• I can't sign in to my Microsoft account
• Why can't I log in to my Outlook account? - Microsoft Q&A
• Can't log into Hotmail on Firefox anymore - Microsoft Q&A