Please fill in the blank with the Base URL which can be found in your backoffice.
System>Configuration>web>Secure (with scope Default Config)
The license key is valid for a single installation of Magento, defined by the BASE URL value in the Backend.
Make sure that your URL ends with "/" (slash)

Multi-website, multi-store, and multi-store view configurations work with the same license key.
This price includes all updates and upgrades of NitroGento extension.