Thanks for bringing this to our attention. I'm here to help you with this but I'll be needing more details.
May I know the name of your financial institution or if you're getting a specific error message? This is for me to check if the problem is caused by a connection problem between QuickBooks Online and your bank.
For now, we can perform basic troubleshooting steps that can help us sort out the problem. Switching to a different browser or clearing your browsing history to update your network can also help. Aside from that, you can manually update your bank account in QuickBooks Online:
Go to Banking from the left menu.
Select the Update button in the upper right-hand corner.
I'll keep an eye to your reply. It's my priority to make sure you're able to use QuickBooks with ease.