The 8-digit number is the so-called voucher code (coupon code), you can redeem it on the homepage of DrawCut under the tab "Prices/Downloads".
To do this, select the required or purchased version of DrawCut under Full Version, e.g. DrawCut PRO, and first click on the "Buy" button.
Now a new window opens, where you can redeem the voucher code in the left field, so that you do not have to purchase the software again.
After the voucher code has been redeemed, DrawCut will send you an automatic mail with your 26-digit PSN, which you can use to activate the license during installation.