Internet access is required for all Marvelous Designer license types with the exception of the Enterprise Network Offline License users.
Please try restarting Marvelous Designer, or restart your computer. If you are still facing difficulty logging in, please make sure you do not have a VPN turned on.
Offline login is available to Marvelous Designer 5-9 users with a perpetual license. If you need to activate license in offline environment, please refer to this manual page