This information is found on the SmartSound website here:
SmartSound Sonicfire Plug-in for Studio activation codes are assigned to a specific serial number. If your purchased code is not accepted, you most likely are using a different serial number than the one that was provided with the order. You can enter your correct serial number by clicking the Help menu and choosing "Change Serial Number". Enter the serial number that was provided with the plugin activation code, then enter the activation code again and it should unlock the plugin features.
If you purchased the Avid/Pinnacle Studio Plugin from Avid or Pinnacle, they will have assigned you a free Express Track serial number along with the corresponding activation code. If you already own the Scoring Edition of Sonicfire Pro, we will need to assign you a new code. Please forward your purchase confirmation to firstname.lastname@example.org and they will verify your purchase and reassign your activation code.