Hi there, Robert_Benjamin.

I'd like to help and share what some insights about the error you encounter when connecting a third-party application to QuickBooks Online.

You can check your antivirus settings, as it may be blocking your apps connection to QuickBooks Online.

You can also use a private browsing window to overcome irregular browser settings.

These are the keyboard shortcuts to open a private window for browsers:

• For Google Chrome and Microsoft Edge press CTRL + SHIFT + N.
• For Mozilla Firefox press Ctrl + Shift + P.
• For Safari (Mac) press Command + Shift + N.

If everything looks good when using the private window, you can go back to your regular browser and clear browser cache. This process will help you fix browsing issues and remove some outdated temporary internet files.

Get back to me if you still have other questions about it. I'm always here to help. Have a great week!