Error 'There was a problem with your authentication attempt' in Files Connect Office 365

Before troubleshooting, confirm that your Files Connect setup follows one of the official Salesforce setup guides:

• The Files Connect Setup Process
• Salesforce Files Connect Implementation Guide

After completing the authentication flow, check the Administration Authentication Status field in the External Data Source record in Salesforce. Then follow the appropriate scenario below.

Scenario 1: Administration Authentication Status Shows "Authenticated"

If the status is "Authenticated," the Token Endpoint URL in the Authentication Provider is likely incorrect.
To confirm, go to the Authentication Provider detail page and copy the Test-Only Initialization URL (found at the bottom of the page). Paste this URL into your browser. If your Authentication Provider is correctly configured, the browser returns an XML file containing an org_id and portal_id. If you do not receive the XML file, the Authentication Provider is not correctly configured.
To fix this, verify that the Token Endpoint URL is exact, including all characters. Even a small typo will prevent authentication from working.

A correct example would be:

https://accounts.accesscontrol.windows.net/mytestsite.onmicrosoft.com/tokens/O
Auth/2?resource=00000003-0000-0ff1-ce00-000000000000/mytestsite.sharepoint.com@my
testsite.onmicrosoft.com

Scenario 2: Administration Authentication Status Shows "Not Authenticated" or "Pending"

If the status is "Not Authenticated" or "Pending," the user account used to authenticate does not have sufficient access to the SharePoint Site Collection defined in the Authorize Endpoint URL.
To resolve this, verify the following:

• The Authorize Endpoint URL in the Authentication Provider points to the SharePoint site collection, not the target site itself.
• The user has at least View-only access to every site in the hierarchy between the site collection and the target site — including the site collection and the target site.

For example, if the target site is:
https://companyname.sharepoint.com/sites/site_collection_name/subsite1/subsite2/subsite3/target_site
Then the user must have at least View-only access to: site_collection_name, subsite1, subsite2, subsite3, and target_site.