They will manually run a database query on Tenable’s backend to disassociate the activation code from the stale Challenge Code. This takes 24–48 hours for Standard support, 2–4 hours for Premium.
You wiped the OS (Windows/Linux) and reinstalled Nessus. The hostname or network configuration changed slightly. The new Challenge Code does not match the old one. Tenable rejects the attempt because your license key is already "Checked out" to the previous OS install. nessus offline activation license already in use
Because offline licenses are manually tied to a unique hardware fingerprint, any change in your system configuration or a previous failed installation can block a new activation attempt. They will manually run a database query on
For the changes to fully process, restart the underlying daemon: systemctl restart nessusd nessus offline activation license already in use