If you have Microsoft Multi-Factor Authentication enabled, Outlook and other applications may not accept your password. This is due to the application not 'understanding' modern authentication.  If you are prompted for a password, then try following this guide to update the Office application first >> Update Office 365 Applications

If Outlook is not connecting and showing a password prompt, use the instructions below to create a single-use application password.

Creating an Application Password

1:Once logged in to your office portal (Sign in HERE) at the top right, click on your little Circle (1) and then Edit 
Account (2)
2: When this page loads, click on (3) Security Info

3: Click on Add method (4)

4: When this window pops up click on the Drop Down (5) and the select App password, then click on Add (6)

6:Type in a description in (7) for the password, like Outook Password and then click on Next (8) 

7:Microsoft will then generate you a password, copy that password (9) and once you have it click on Done (10)

It is worth adding that password to a text file temporarily on your desktop.
This is because, Outlook may not prompt for the password immediately.
Once Outlook has requested the password and it is working, you should DELETE the text file that has the app password in.

8:You will now see that App password listed, the only option you have is to delete that password.

Note: You will only ever see the password once, so once you have created it, it cannot be revealed again.

Using the password

You can now enter that password into any Microsoft Application that is not accepting your password and MFA code.

For example, Microsoft Outlook:
  1. Check that is your  (1) email address.
  2. Paste in your password (2) App Password.
  3. Check the Remember my credentials (3).
  4. Click on OK.
  5. If you have saved that password in a file, you should DELETE it. You can always create another one.