If I want to enter expense input I get a error message?
Welcome to the Community, @pieterschultz188. Let's work together to get rid of the error.
Sometimes your browser holds too much app data and add-on's that causes unusual behavior of the program. This is why you're getting an error while creating an expense. Let's access your account via a private browser to confirm.
CTRL+SHIFT+N for Chrome.
CTRL+SHIFT+P for IE and Firefox.
Once done, log in to your QuickBooks account and create an expense. If it's working fine, go back to your regular browser and clear its cache.