Hello Mabreor,
If your iPhone won't connect to an Apple Watch, the first thing is to check the connections that message is referring to. On the phone go to Settings, and make sure you have both Wi-Fi and Bluetooth turned on.
If you still get the same error messages when trying to use the Watch app, restart both devices.
Restart your iPhone
Restart Apple Watch
You'll also want to make sure Airplane mode is not currently enabled in Control Center on the watch.
If your Apple Watch isn't connected or paired with your iPhone
If it still won't connect, then you can reset and re-pair the watch.
Unpair and erase your Apple Watch
Set up your Apple Watch
If none of those steps are able to get the Watch app to connect with the Apple Watch, you'll want to contact Apple for assistance: Get Support
Cheers!