If your scanner lacks internet access, you must generate a "challenge code" using nessuscli fetch --challenge and provide it along with your activation code at the Tenable Offline Registration page.
This is the easiest answer to "nessus get activation code" for beginners. nessus get activation code
| Issue | Solution | |-------|----------| | “Activation code invalid” | Make sure you downloaded the correct version (Professional vs. Essentials). Codes are not interchangeable. | | Free code expired | Go back to the Essentials registration page with the same email → get a new code. | | No email from Tenable | Wait 5 min, check spam, or use a different email (Gmail works best). | If your scanner lacks internet access, you must
No. The 14-day Nessus Professional trial requires only an email and organization name. No payment details are needed. Essentials)
If you are a professional needing to scan more than 16 IPs or requiring compliance reporting, you cannot simply "get" a code for free online. Nessus Professional is a commercial product.