You are using phpFox version earlier than 4.6.0? Please refer instruction for this article here.
When upgrading your site, or posting reviews at our store, you will be asked to enter your site's License ID and Key. This information is emailed to you when you first purchased a license. If you have lost this information, you can retrieve it from here. Just click your license in the "Your Active Services/Products" block:
You will then be brought to the page that shows your license ID, Key, domain name and download link:
If you would like to change license key as well as license domain, you can click on "Reset License" button on this page. A new license key will be generated and associated domain will be removed right then.
Access license key from web server