SEOUL, Nov 3 (Reuters) - South Korea"s Kakao Pay Corp (377300.KS) saw its shares double in value from their initial public offering (IPO) price on their trading debut on Wednesday, as the fintech"s expected growth in transactions and other services whetted investor appetite. Kakao Pay shares opened at 180,000 won on the KOSPI (.KS11) versus an IPO price of 90,000 won, and gained to 187,500 won in early trade.The financial technology firm raised 1.5 trillion won ($1.27 billion) from its IPO. China"s Ant Group-backed Kakao Pay plans to use 854 billion won ($724.66 million), or about 56% of the funds the company raised after costs, for mergers and acquisitions, it said in a regulatory filing.Kakao Corp (035720.KS), operator of South Korea"s dominant chat app, remains a major shareholder with around a 48% stake. Ant Group"s Alipay Singapore Holding has a 39% stake, and some of its shares can be traded without a lock-up period. Having started payments service in 2014, Kakao Pay saw annual transactions grow from about 48 trillion won in 2019 to 67 trillion won in 2020. Transactions will likely grow sharply to around 100 trillion won in 2021, analysts said. Kakao Pay had pushed back its IPO to November and slightly lowered an indicative price range after South Korean regulators said financial services platform apps needed to register or be licensed to provide financial product comparison and recommendation services. read more "Regulation can be a new opportunity to gain more consumer trust," Kakao Pay chief strategy officer Shin Won-keun told a news conference last week. Besides raising money for M&A, it is also preparing mobile stock trading services and seeking partnerships with global fintech companies to target potential overseas markets such as China, Southeast Asia and Europe, Kakao Pay said. Outsized domestic retail investor demand has fed a boom in South Korean IPOs this year and increased volatility for newly-listed firms. The IPOs have raised more than four times the funds they did in 2020. read more ($1 = 1,178.8900 won)