How to resolve NSURLErrorDomain:-1 error with Microsoft 365 accounts and OneDrive on Safari?

Ok, thanks.

I have some suggestions for you to try.

Since OneDrive and Microsoft 365 rely on authentication cookies, clearing old or conflicting cookies can help, so yes, doing so would be a good first step.

The next suggestion would be disable any Safari extensions, especially ad blockers (or privacy-focused ones) as they can interfere with Microsoft 365 logins.

Next look for corrupt or duplicated credentials in Keychain Access:

• Open Keychain Access (Note: On my Mac, running macOS Sequoia, Keychain Access did not appear as an icon in the /Applications/Utilities folder. In order for me to access it I had to enter Keychain Access into Spotlight).
• In the Login keychain, search for Microsoft and OneDrive.
• Delete any saved passwords or tokens related to Microsoft 365.
• Try logging in to OneDrive again in Safari.

Next, test in Private Browsing Mode

• Open Safari > File > New Private Window.
• Try accessing OneDrive and Microsoft 365. If it works, the issue is likely related to cookies or cached data.

Next, since you have multiple Microsoft 365 accounts, Safari might be struggling with authentication:

• Sign out from all Microsoft accounts at https://account.microsoft.com.
• Restart Safari.
• Sign in to one account first and test OneDrive.

Next, try flushing the DNS cache on your Mac.

• Open Terminal and run:

sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

• Restart your Mac.

Finally, check if the issue is with Apple’s Safari Tracking Prevention

Safari’s Intelligent Tracking Prevention (ITP) might be causing conflicts with Microsoft authentication.

• Go to Safari > Settings > Privacy.
• Uncheck Prevent cross-site tracking.
• Restart Safari and test OneDrive again.

Let's start with: Is this issue only with the Safari web browser? Does this issue still occur with another web browser? What device are you using when you see this error: Mac, iPhone/iPad, Windows PC, etc.?

The NSURLErrorDomain:-1 error in Safari when using Microsoft 365 and OneDrive is often related to authentication issues, cookies, or conflicts between multiple Microsoft accounts.

If this issue is only with Safari, have you tried clearing its cache & cookies (specific to Microsoft)?

Thanks, but before I accept it being as such, let's see if any of it actually helps. Please give them a try, and let us know what did, and didn't work. I try to keep updated notes should someone else come across this same issue. TIA.