Update: Finally succeeded…

Order of actions upon visiting the site = Log into your account FIRST, then in the PRISM Drums Lite page, click on “More payment options” instead of “Add to cart”. See if this works for you.

Nope, still fails to redeem, because any attempts to access the store Cart results in an error that makes the entire site inaccessible until cookies are cleared. Checked in both Firefox & Chrome.

So, i’m still failing to redeem this freebie after 3 days. :(

Update: It was some kinda problem with account-registration that made the site completely inaccessible. Using a New Private Window within Firefox made it accessible again.