In just two years, Chinese-owned Temu has come out of nowhere to become one of the best-known bargain shopping sites, known for its ultracheap and sometimes wacky gadgets and apparel. U.S. consumers are expected to spend about $18 billion on the site this year. Behind the scenes, though, Temu has encountered trouble with the bank that was handling those payments. Citigroup, the fourth-biggest U.S. bank, stopped handling payments for Temu in the U.S. late last year, just a year after the site's launch, following questions raised about Temu's business by payments network Visa, according to people close to the situation. Visa wanted to know whether Temu was doing enough to ensure merchants weren't selling counterfeit or illegal goods.