New Delhi, June 26 -- LOS ANGELES - For the collectors who spent hours watching live streams on Whatnot, clicking to buy a spot in a randomized card break, the experience felt like retail shopping. Now, a California attorney says it was gambling, and 30 of his clients want their money back.

Attorney Paul Lesko filed 15 arbitration claims in March against Whatnot, the Santa Monica-based live-shopping platform that generated more than $8 billion in sales last year and sells roughly six million trading cards per month. The complaints allege that Whatnot's core card-breaking format, where users pay for a "spot" and a randomized digital tool determines which team or player they receive from an unopened box, constitutes an illegal lottery unde...