Arc cannot generate the license if the browser you are using does not have internet connection.
You will need to find a browser which has access to internet. Then access Arc replacing in the URL localhost with the server name where Arc is intalled (http://servername:7070).
Click again the Buy Now button and you should now see this:
You can now go to the Request License tab, enter the customer ID received by email or enter the email used to buy the subscription:
After clicking the request license button, an email will be sent (from email@example.com) to the email used to purchase the subscription with the License ID:
To validate the license, copy the License ID from the email and paste it in the Validate License tab:
If the Buy Now button disappears, it means that your license is now active.