Hello Bhushan-
Thanks for your reply! Could you please try connecting to your lab again and let me know if you are able to connect? We experienced a brief outage.
If you still get the error "The VPN connection failed due to unsuccessful domain name resolution" could you please ping 'devnetsandboxlabs.cisco.com' and let me know what IP address is resolving?
Please let me know if you have any questions!
Jacob