Hi,
Please ensure you have downloaded the installer from your account.
Once done please look over the following :
To activate Studio One using the online method, please follow the instructions located in the following knowledge base article:
https://support.presonus.com/hc/en-us/articles/360043921991--3-Studio-One-5-Software-Activation-Online-Computer-
If you continue to have issues please contact Technical Support.