This error is often a sign that your Microsoft Account (Outlook.com) security information—specifically the recovery options—needs to be updated or completed.
Here is the error message you received and step-by-step instructions on how to set or update your recovery options.
🛑 Error Message
The exact error you are receiving is:
"The browser based authentication dialog failed to complete. Reason: The request could not be processed by the server due to invalid syntax."
This error typically appears when an application attempts to use a modern, browser-based sign-in method to connect to your Outlook.com account, and the Microsoft server rejects the request, often due to an incomplete or outdated security profile.
✅ Instructions to Set/Update Recovery Options
You need to access your Microsoft Account security dashboard to verify and set up your recovery options.
Step 1: Access Your Microsoft Account Security Page
Sign in with your affected Outlook.com email address and password.
Step 2: Navigate to Security Info
Once signed in, you should see your main security dashboard.
Click on the "Manage how I sign in" tile or link.
Step 3: Add/Update Your Recovery Information
On the " Manage how I sign in" page, you will see a section titled "Ways to prove who you are." This is where you set your recovery options. You should have at least two different methods set up.
Add a new way to sign in or verify: Click this link to see the available options.
Add an alternate Email Address:
Choose "Email a recovery code."
Enter an alternate email address that is not the one you're having trouble with (e.g., a Gmail or a work email).
Microsoft will send a verification code to that alternate email. Retrieve the code and enter it on the Microsoft site to confirm the address.
Add a Phone Number:
Choose "Text a code" or "Call me."
Enter your mobile phone number and choose your country code.
Microsoft will send a text message with a verification code. Enter the code to confirm the number.
Confirm your existing options:
Step 4: Finalize and Test
After adding or updating your recovery email and/or phone number, you may need to scroll down and click "Save" or just close the browser window (changes are typically saved immediately).
Sign out of your account on the web browser.
Go back to the application where you received the login error (e.g., Outlook desktop, an email app) and try to sign in or re-authenticate your Outlook.com account again.
The presence of complete and confirmed security/recovery information often resolves authentication issues, allowing the browser-based sign-in dialog to complete successfully.