What is the name of the domain?
1.1.1.1
What is the error number?
404
What is the error message?
Your Tunnel Configuration is Invalid
What is the issue you’re encountering
VPN not Connecting
May I ask if it’s a new installation or? 
Are you using the latest version of the Warp app for your mobile?
May I ask if you’ve tried the steps as described from below?:
If not, try to go to the Settings/Preference > Connection > Reset all connection.
Could be you have to clear storage & cache data from the app, delete the app and re-install again. Have you tried it already?
I solved the same problem going to Cloudflare Dashboard > My Team > Devices. Then in devices i have noticed that more then one register for the same device (my phone in this case). Just revoke this devices. Before that, I also logout from the app on my phone, then login again, and problem solved.
Ive got this problem on 3 Android devices. (They all have GSF running) Tried different Wifi networks (Work and home) but still the same. Reset - Reinstalled - No luck - “Tunnel configuration is invalid” error. I get Device not registered if I switch on Warp. Accoutn key blacnk - And I cannot enter a Account Key from the last and only device I have left that is actually working - too scared to paly with it in case I loos that one as well. Hope this gets resolved. ITs not a device issue - Like I said - its happening on 3 of my 4 devices.