Bootcamp Windows 10 does not validate product key

I just recently downloaded windows 10 through boot camp. I followed all the steps required to install windows 10 through boot camp correctly. I purchased a valid product key online. When I was prompted to enter the product key it says the key was invalid. Is there a reason why this happened because I bought the key from a reputable site. I skipped the option to enter the key after that and let everything install and setup. I went to my Control Panel and looked for a place to activate windows with a product key and it did not work there either. Any thought on why this is happening and how I can get my product key to work?