Let's get your bank connected to QuickBooks Online, director-isabell.
What specific error message or code did you receive when connection your bank account? This would help us know what troubleshooting steps we can do to easily connect your bank.
Meanwhile, here are the three possible reasons why you're unable to connect your bank account. It could be that:
You can browse this link on how we can get this working: Find your bank or credit card account when you connect to online banking.
Once you have connected your bank account, you can already categorise the downloaded bank transactions.
Here's another link that you might find helpful when troubleshooting Bank Feed issues: Troubleshoot issues with Bank Feeds.
Let us know how the connection process goes so we can further assist you.