If you have finished paying your Studio One least, you will first need to upgrade your Studio One license via PreSonus’ my.presonus website before inputting your serial into Studio One:
Log into my.presonus.com
Select Products > Software
Select Studio One Professional OEM
Click the blue "Upgrade" link under the serial number that you are upgrading.
After clicking the "Upgrade" link, please click the link that reads "If you have an upgrade key, enter it here"
Your product key will be shown here: splice.com/plugins/your-plugins
Paste or enter the new product key and click “Register Upgrade Key.”
From there, please open Studio One on your computer and go to Studio One > Studio One Activation. Activate with the new code that you just registered. Below are guides with instructions on activating: