You may get the error for various reasons. 

1.  Please make sure the purchase code is valid. Find the purchase code in your codecanyon download section.  
2. Sometimes, there could be problem in server. So try after sometime and see if that work or not. 
3. You can use a purchase code for one site only. If the same purchase code is used on multiple sites, please remove it from all other installations and keep it on only one site. If you are using RISE 3.9.4 or later and want to use the purchase code on another site, first disable the purchase code from Settings → Updates on the current site.

For any help, please contact via the the Support page.