Can you please try activation using Command line option as mentioned below?
Through Windows Command prompt, you can execute different commands associated with subscription licensing like activating, deactivating, viewing licenses, etc. Please find below the steps to execute these commands:
1. Launch the Windows Command Prompt from the start menu by typing "cmd". Right click the Command Prompt application and select Run as Administrator.
2. In the command prompt, type in:
cd C:\Program Files\ANSYS Inc\Shared Files\Licensing\winx64
(this is the default installation directory of Discovery products. If you have installed it at a different location, enter the appropriate path where ansysls_client.exe is present)
3. Once in that directory, run the following commands: ansysls_client.exe -ActivateLicenseEntitlement < ActivationID >
This command can be used to activate license on your machine. In above command, replace < ActivationID > with your activation id. You can find the activation id in the txt file that you receive or from your Discovery Account page under Manage Subscriptions section.