If this works, return to your regular browser and clear the cache. This will remove the stored cache or cookies to refresh your browser's background process. If the same thing happens, use another supported browser. It could be that the one you're currently using has a temporary issue with QuickBooks.
Once connected, you have to log out and log in to your account and check the Transactions/Banking menu.
Then, to review each downloaded transactions, you have to categorize and match them into QuickBooks Online.
Keep me posted if you have any other concerns about connecting your credit card to QuickBooks. I'm always here to help. Have a great day ahead.