Existing Stardock Account
You can log into your account and purchase additional activations for any key - for example:
Resellers
If you are a reseller trying to purchase additional activations for a client and their key, go to the product page for the product and select the business option. From here click on the Add activation to an existing key link found under the Single Key and Multiple Keys options
This will then take to a page to validate the user key and continue the order process
