Typehint IP2LocationIO\Configuration

[jmwebservices]

You can save boilerplate code in the IP2LocationIO\DomainWhois, IP2LocationIO\HostedDomain, IP2LocationIO\IPGeolocation constructors by type hinting the $config parameter.

public function __construct( Configuration $config)
{
	$this->config = $config;
}

[jmwebservices]

I would also consider setting $apiKey to private in IP2LocationIO\Configuration and creating a getApiKey method to retrieve its value. In order to be backwards compatible, you can implement the magic __get method so that retrieving apiKey as an object property is still possible.