Thank you for dropping your question here in Community, @sarahmangold8.
The JSON error mostly caused by a QuickBooks Online app or a web browser. To fix this issue, I recommend using another browser or a private browser/incognito window so you would identify the root cause of this error.
If you were able to log in, lets clear the cache of your default browser so you will have the best and most secure experience with QuickBooks Online.
To clear cache, here’s how.
Google Chrome
Select the Menu: button.
Select Settings.
Select Advanced.
Select Site settings under Privacy and Security.
Select Cookies and site data.
Select See all cookies and site data.
Type “intuit” in the search bar to find Intuit cookies.
Select Remove.
Restart Google Chrome for the changes to take effect.