HI Leemc-84,
Thank you for your post, welcome to the Community Forums.
I'm sorry to hear you're having some trouble with the Connect App. Can you please first try factory resetting the Hub 4 - to do this, you'll just need to push in a pin into the pin hole at the back of the Hub for 30 seconds.
Do you have a screenshot of the exact error? Is it not saying that your Hub cannot be located?
I'd also try deleting the app and redownloading it again, and also forgetting your old Hub credentials on your device.
Let us know how you get on with those steps 🙂
Beth