The following error has occurred: Unexpected token < in JSON at position 0

I'll help you fix the error,

You will get this Unexpected token < in JSON at position 0 error when the URL doesn't exist. It's possible that there's an extra (or missing) character on the link.

If you're getting this message when opening QuickBooks, let's try using the incognito or private browser. This mode won't retain your temporary browsing data, history, search records, and cookies.

You can use these keyboard shortcuts:

• Google Chrome: Ctrl + Shift + N
• Mozilla Firefox: Ctrl + Shift + P
• Safari: Command + Option + P

Then, sign in to your QuickBooks Online account. If you're not getting the error message, please open your regular browser and clear its cache. Clearing your cache helps to troubleshoot and improve your browser's performance.  Restart your browser after.

On the other hand try using a different supported browser.

I'm always around if you need anything else. Just click on the Reply button below, and I'll get back to you as soon as I can. Thanks.