"Froala recently changed their licensing for OEM, with an option that will allow us to include licensed copy with all UNA cloud accounts and all Pro subscriptions. This should be available in 13b1. In the meantime you can email support (firstname.lastname@example.org) to arrange direct activation."
An OEM license refers to the license that a manufacturer installs on new devices. If this is your case, the product key isn't transferable, and you can't use it to activate another installation. (Unless you're re-activating a new installation on the same computer.)