LULU xPRESS via Shopify requires buyers to register?

Hi...just installed a buy button into a Wordpress page to enable purchases and when click either Buy or Add to Cart to test, for the 2 different checkout type options (inserted their html for the button copy/paste), I get told the buy isn't enabled because a plan and credit card haven't been chosen. Just want to make sure I'm getting this right....to use Lulu xPress, registration at Shopify is required for all buyers before they can do the purchase? Also, since the message isn't chock full of info, it would be nice to know exactly what plan they are talking about. Perhaps the plan i just chose when I set up the Shopify store and it's not being seen?

If yes, is there any way to do a purchase where the buy button goes straight to a payment page without other hoops for the buyer to jump thru? Is that what comes with using the API interface
tnx