Floating licenses should be activated in the Geneious Floating License Manager, not in Geneious itself. The Floating License Manager (FLM) is a FLEXnet license server and must be installed on a server with a fixed IP address that all Geneious client computers can connect to. You will be prompted to activate your license during the FLM installation.
Once the Floating License Manager is installed, download and install Geneious on each computer that will be using the software.
To connect Geneious to the Floating License Manager, start Geneious and go to Help->Activate License. Check "Use floating license server" and enter the address and port (default 27001) for the computer where the Floating License Manager was installed.
You must have both ports (default 27001 and 49630) open on the client machines in order to connect to the license manager.
Floating License Manager Installers
Floating License Manager User Manual
Note: To install on MacOS, users must first download and install the Java 8 JDK from http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html. This must be installed prior to running the Floating License Manager installer.
Note: if you received your license key as a text file, you do not need the floating license manager. See this post for further information.