Thanks for providing the error code, bjebelli.
I reviewed our system to see if we have issues related to this but I've found nothing. I'd recommend reaching out to your bank to verify if they have an ongoing website maintenance (which probably is causing the issue).
After that, you can try connecting Costco to QuickBooks Online again. If the same thing happens, we can do browser troubleshooting steps to get rid of any cache-related issues.
You can use a private browser since it doesn't store cache files. Other browsers are good alternatives, too. If you can connect successfully, I'd recommend clearing the cache storage of your regular browser.
Otherwise, it's best to reach to our QuickBooks Customer Care Team. They'll be able to pull up your account and do further troubleshooting steps. You can reach them through this link: Get Help with QuickBooks Online.
I'll be right here if you need anything else.
