BEIJING, Oct 8 (Reuters) – China's antitrust regulator has fined food delivery giant Meituan (3690.HK) 3.4 billion yuan ($527.4 million) for abusing its dominant market position, the watchdog said on Friday, the latest penalty in Beijing's clampdown on online platforms. The fine equates to 3% of the company's domestic sales in 2020, the regulator said, adding that Meituan should stop its "illegal behaviour" and return 1.29 billion yuan to merchants on its platforms. Meituan said it accepted the penalty and will implement the rectifications ordered by the regulator. The State Administration of Market Regulation (SAMR) launched an antitrust investigation into…