Sometimes the stored browser in your data is the cause of this error. I suggest clearing the browser's cache to isolate this. You can use the incognito browser to check if you can cancel it there and go back to your regular browser to clear the cache. An alternative way is to use another supported browser in QuickBooks.
Here are the shortcuts keys for opening an incognito browser:
Google Chrome: Ctrl + Shift + N
Safari: ⌘ + Option + P
Internet Explorer & Mozilla Firefox: Ctrl + Shift + P
If you can see the same error, I suggest contacting QuickBooks Customer Care team to verify and check further what has caused this issue to point out what specific resolution can be done. You can also ask them to cancel your subscription.