This article covers troubleshooting steps if you are unable to register a SonicWall firewall.
The following are a few troubleshooting methods that may resolve firewall registration issues:
Browser cache may be displaying invalid information. Be sure to clear the browser's cookies and cached pages while testing.
Ensure you are using an updated browser.
Ensure the DNS on the firewall is resolving names properly. To register, the firewall needs to contact licensemanager.sonicwall.com. If it fails to resolve licensemanager.sonicwall.com, test alternate DNS settings.You can change the DNS under the Network | DNS page to public DNS servers such as 220.127.116.11, or 18.104.22.168. Please see article: How to use "DNS Name Lookup" diagnostic tool to resolve Name Servers.
Adjusting the MTU may also prove useful. For complete information on adjusting the MTU value in the appliance, please see article: How to change the MTU size.
Ensure that there are no other devices between the firewall and the internet that may be filtering or blocking traffic.