Why is "free license" displayed under "Help -> About -> Account license"?
You are holder of a Business license:
That is the way it supposed to be, as the Computers & Contacts list does not recognize the license of the TeamViewer main program. Therefore, although it says Free you can use it unrestricted.
You are holder of a Premium- or Corporate license:
Please activate your license in the Computers & Contacts list or in the TeamViewer Management Console.
Computer & Contacts list:
Please click on the Computers & Contacts icon on the left side of the TeamViewer main screen. Please login on the right window using your username and password. If you do not have set up an account yet, please do so now under Sign Up.
When then logged in, you can activate your license in the options of the list under Edit profile. Please enter your license key in the new window.
Navigate to the TeamViewer Management Console and log in to your TeamViewer account. Click on the upper right corner on the light blue button and choose Edit profile. Here you can activate or change your license: