Yeah, costco is a membership club. If you aren’t a member/don’t want to be one you can bypass that restriction by having a friend who is a member order it for you
Sam’s (also a member club) has the tv for the same price:
Buy VIZIO 58" Class V-Series 4K HDR Smart TV - V585-H : 48" - 58" at SamsClub.com
www.samsclub.com