Bellow are the steps for checking whether a 3.x license is correct:
1. Check the licensed domain. Note that the license key is tied to the top level domain name. You can view your key details from License Keys > Show key file link at Your Account.
2. Make sure the company name is spelled correctly.
3. Make sure that your license key is in a file named LicenseFile.xml.
4. Make sure LicenseFile.xml is located in ~/[YourWebsite]/Sitefinity folder.
5. Restart your application when you save the LicenseFile.xml in your project Sitefinity folder. You can restart Sitefinity by making a dummy change in the web.config file
6. To check whether Sitefinity has found any license file for your project, do the following:
1. On the public side of the project, right-click on any website page and open the page source (IE: View Source, Firefox: View Page Source).
2. Locate the meta tag with name Generator. It should look like this: <meta name="Generator" content="Sitefinity 3.7.2096.2:0" /> and check if the digit after the colon is different from zero. If this digit is still zero, it means that no licenses are currently found by Sitefinity and applied to the project. If the last digit is no longer zero, this means that your license key for the registered domain name has been recognized by Sitefinity and your website visitors will no longer get a trial message. That last digit signifies the number of licenses found and applied to a Sitefinity project.
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Sitefinity CMS Ideas&Feedback Portal
and vote to affect the priority of the items