You'd need to look at the 'licence failure report' generated after activation fails:
Could not validate license "DesignSpark " in C:\ProgramData\XHEO INC\SharedLicenses\SCtemp.lic.
An unexpected error occurred while validating.
Too many instances of the MACAddress component to generate a valid hash.
If you see the line in bold, it means there are an excessive number of hardware components which can be used to generate a machine fingerprint to which the licence key is attached.
Open Windows Device Manager (usually in Control Panel)-> Network Adapters. If at a workplace, you may need your IT admin's help with this.
Do you find multiple 'virtual' adapters listed? These could be used for a VPN connection or a hypervisor (like VMware or VirtualBox). Try disabling the virtual adapters and then open DSM again. Enter your licence key and it should activate.
Also, you could try re-installing your Hypervisor (VMware or VirtualBox) or VPN client and this will remove the redundant adapters.
If you require our support agent to assist with the above, please contact email@example.com
with the licence failure report attached.