I had a conversation with the mechanic who set these bikes up. Here are some important points.
His opinion is that these bikes are in the early stages of development, so some things that you might expect from a more prominent e-bike maker may not be there, at least in June of 2025. We expect the firmware/software to improve over time.
The phone app is the main security system for the bike. The bike cannot be started without being paired to a unique phone app installation. This has several consequences. If you don't have the paired phone next to the bike, it will not start. If you have more than one of these bikes in the same household, each must be paired to a unique phone. Each phone app can only be paired to one bike. If you paired your bike to your phone, and switched the pairing to another bike, your original bike will be disabled. If you look at it from a security perspective, it makes sense.
If you have one bike and one phone app, they have been paired, and the bike has been ridden in the past, and you cannot start the bike, it is most likely because the pairing has been lost. We had a customer in for this issue yesterday. What you have to do is pair it again manually. This can be done through the app. There should be a section to "pair manually". Make sure that your bike and phone are charged up. Once the bike is paired to the app again, you should be able to start the bike. You may have to register your fingerprint again as well. If that doesn't work, you'll have to either work with Urtopia or take it to a dealer.
Good luck.