Hi,
Not sure what you are experiencing here. The process as I understand it is... Once you have a product, you set up a "My Presonus account"...here you are asked to register your products... hardware, and software. If you bought the "retail package", the key is somewhere in the packaging, depending on where it was purchased you could find it several places, but it WOULD NOT be difficult to find (but can cause problems) when manually entering the code...
If you have purchased this online, you should be emailed a product code or one should be supplied for you. Here it's best to copy and paste the code into the code field m(if possible) and there are some potential pitfalls, as I recall 'I' and '1' can create issues... this process is best handled, as I said in your "My Presonus account" . Set up an account if you haven't already, and then go to "My software" within your account... download the software and add the product code when prompted. if you continue to have issues, a Tech ticket can help get you the answers you need...