The palettes are in the Store - you use the code to “pay” for one. The contents of the card is in the Downloads page of website - Synth downloads • Polyend . That includes the stock palettes. (I presume you also got a physical SD card - if not you should contact your retailer. Stupidly, I can’t recall whether it came in the Synth already, or in the USB SD card adapter!)
I think you have to enter in the Polyend web page and then go to “Palettes”. Choose the pack you want and click “add to cart”. When you go to the payment in the cart you’ll see this page:
Thank you, @darioleicach.
I was able to apply the coupon by entering the code for the ‘prism’ palette.
Actually, before I asked this question, I had tried the same thing with the ’ Old School Rave’ palette that was on the card, but was confused because the coupon did not apply.