i got error "Something went wrong. [657rx]" cant add office365 accounts to my office 2021 outlook

Hi Alex Kuah

Thank you for posting question to Microsoft Q&A and for providing a detailed description of the issue you are facing with Outlook 2021. 

I understand you are experiencing an authentication loop and are receiving the error "Something went wrong. [657rx]" when trying to add your Microsoft 365 accounts. This issue typically arises from a conflict with outdated or corrupted authentication tokens stored locally on your computer. After an update, Outlook may struggle to use these old tokens, leading to the sign-in loop. We will resolve this by clearing the old data and allowing Outlook to create a fresh connection. 

Here are some recommended solutions you can try: 

Option 1: Clear Stored Credentials from Credential Manager 

This process removes any old passwords and tokens that Outlook may be trying to use. 

• Close Outlook and all other Microsoft Office applications (Word, Excel, Teams). 
• Click on the Start Menu or the Search Bar on your taskbar and typing Credential Manager > Select Windows Credentials. 

Under the "Generic Credentials" section, locate and remove any entries that contain "MicrosoftOffice16_Data". 

Restart your computer and open Outlook and try to add your account again. 

Option 2: Reset the Authentication Broker Cache 

• Close All Microsoft Apps: Shut down Outlook, Teams, and OneDrive completely.
• Disconnect Account:
  • Go to Settings > Accounts > Access work or school.
  • Click your work/school account, then click Disconnect.
• Clear Cached Credentials:
  • Open Credential Manager > Windows Credentials.
  • Remove all items that start with MicrosoftOffice16_Data.
  • In File Explorer, go to %localappdata%\Packages.
  • Rename the folder Microsoft.AAD.BrokerPlugin_cw5n1h2txyewy by adding .old to the end.
• Restart and Reconnect:
  • Restart your computer.
  • Go back to Access work or school > Connect your account again and open Outlook and sign in. It should now work correctly. 

Option 3: Create a New Outlook Profile 

If the problem is tied to a corrupted profile, creating a new one provides a clean slate without deleting any of your server-side email data by following this article.

Create an Outlook profile - Microsoft Support

If the issue continues after following these steps, please let me know in the comment section. I will be very glad to support you

Wish you a pleasant day!

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