Business-to-business payments platform Nium announced Monday that it raised more than $200 million in Series D funding and saw its valuation rise above $1 billion. The company, now Singapore-based but shifting to the Bay Area, touted the investment as making it “the first B2B payments unicorn from Southeast Asia.” Riverwood Capital led the round, in which Temasek, Visa, Vertex Ventures, Atinum Capital, Beacon Venture Capital and Rocket Capital Investment participated, along with a group of angel investors like DoorDash’s Gokul Rajaram, FIS’ Vicky Bindra and Tribe Capital’s Arjun Sethi. Including…