Question: I can't get a license for additional domain
1. First, please make sure you've logged in using your paypal email address
2. Check "My Purchases" section, which should list all your recent purchases
3. If there is a purchase listed, which doesn't have a link "Specify Domain Name",
it probably means, that you bought a "Single Domain License" which was on sale in the past.
One way how to confirm this is fact - is to check your purchase receipt,
or if the price of your purchase you made in the past is the same as one on purchase (buy now) page
If you plan to add additional domains, it's worth to purchase the multi domain license.
Then, you're able to add as many domains as you want and install the software there