Welcome to the Community. I'm here to help you connect your clients' bank accounts in QuickBooks Online.
Once there's an update, your bank communicates with QuickBooks to ensure accounts will connect successfully. I suggest you perform some troubleshooting steps to validate the issue happening on your end.
You can start by logging in to your bank's website using the correct credentials. Check if there are no issues with accessing the account outside QuickBooks.
If it works fine, copy and paste the login link from the website to the bank search box in QuickBooks (see screenshot below). It will help ensure you're connecting to the correct financial institution.
In case they have an ongoing maintenance update, you'll want to wait it out until they finish it. After the maintenance, connect with Nedbank again.