Activate Smart Designer (Legacy)

        1. Open you CorelDRAW   

        2. Go to the activation tab on the right hand side in the Command Center/Smart Designer.   
        3. Click the "Click to Activate" 
        -If needed, click Remove License first to make this appear 
        4. Copy and paste the serial number provided to the activation window in the middle of the work area.    
        5. Click Apply and follow the final instructions.   
        6. Restart CorelDRAW.

For any activation error you are going to go into the Activation tab and try activating with the serial number. In that activation window it will either take the serial number or tell you a more detailed error. If you get a more detailed error, please take a screenshot and submit a support ticket if you already have a support ticket dealing with this issue attach it to that email. 

(How to take a screenshot)