Why can't I link my Capital One accounts to QBO?

Try opening your QBO account on any private/incognito browser.

Hello, @hiseancarroll-gm. I appreciate you bringing this issue to our attention and for trying to fix the error by doing some troubleshooting steps. I'm here to provide you some details about this error.

Currently, we have an ongoing investigation for this exact issue you stated above. Our engineering team is aware of this issue and doing their best to fix this as soon as possible. Then, please reach out to our QuickBooks Support Team. So that, they can add your company to the list of affected users and you'll be notified about the status of the issue via email.

Here's how:
 

1. Sign in to your QuickBooks Online company.
2. Go to Help.
3. Choose Contact Us.
4. Type in your concern, then click on Let's talk.
5. Select a way to connect with us:

• Start a chat with a support expert.
• Get a callback from the next available expert.
   

You can refer to this article for the time schedule: Contact Support in QuickBooks Online.

I've also added this following articles for future references:
 

• Categorize and match online bank transactions in QuickBooks Online
• Reconcile an account in QuickBooks Online
   

I'll be around if you have any other concern of if you have clarification with your banking issue. Take care always!