Hello there, nicola19. I understand the importance of connecting your bank to QuickBooks Online (QBO). I'm here to help you figure this out so you can continue with your tasks.
As per checking here on my end, there's no reported connection issue with your bank institution. May I know if you encounter a specific error message, so we can check further and provide the exact resolution to this concern. You can also perform some troubleshooting steps based on the error message you encounter in this article: Open Banking connection errors in QuickBooks Online.
I has trouble starting midnight Thursday and most of yesterday and asked for a QB call (came within seconds!). They talked me through disconnecting and reconnecting my bank - thank you QB. This worked BUT when it reconnected I got a couple of duplicate transactions (one income, one expenditure dated over the previous three days) which I had to Exclude. So someone has had problems. Touchwood all is OK today.