Afterwards, the key can be used on any IP, but only on one server at a time. You need to have the IP match the public IP on which you're going to first use the key.
Make sure you have registered a license key on the Cfx.re Keymaster service.
Having trouble running your server? Visit server issues, use the Discord #fxserver-support channel or create a topic in the Server Discussion sub-category on the forum. FXServer is the name of the Cfx.re platform server.