Welcome to the Community forum, @sunjayc. I'll share some troubleshooting steps to help you fix your credit card connection issue in QuickBooks Online (QBO).

Since you're done trying to disconnect and reconnect your Halifax credit card account using a private window in a Chrome browser. We can also try to clear your browser's cache before performing the reconnection process. Clearing the cache or cookies is the best way to get a clean slate for your browser. Otherwise, using other supported browsers can be a good alternative too.

If you try the above and find you are receiving an error message, if you could go through the steps on this guide: Open Banking connection errors in QuickBooks Online.

If you still find that error message shows after following the help article let us know.  We will take a look and make sure we get a resolution for you. We're always here to help you out. Have a good one!