Please see this article for all the possible ways of activating your Little Green Button.
If you just need an activation key, please obtain this from The Little Green Button Management Site's Activation tab. You will need to have access to the management site with a minimum role of User to view this.
If you are trying to install Little Green Button from scratch, but have lost your activation key, please get in touch with us and we can supply you with one.
Please supply sufficient information for us to find your subscription, like the email address used to register, company name, invoice number.