Hyundai Sonata 2012, 52,000 Miles: P0087 Fuel Rail Pressure Low - Hard Starting and Engine Light On

My friend's 2012 Hyundai Sonata (52,000 miles) has been displaying a P0087 fault code indicating low fuel rail pressure. This vehicle is equipped with a gasoline direct injection (GDI) system, which uses a newer fuel delivery setup compared to older models. The car runs fine under normal conditions, but the check engine light remains on and it experiences significant difficulty starting—especially in cold weather. Once started, it starts but requires prolonged cranking. The battery and starter have been checked and are functioning properly. The vehicle was previously repaired after a rear accident and has accumulated approximately 20,000 miles of post-repair driving with no prior issues. We recently replaced all spark plugs with the same type, and upon inspection, several showed signs of burn marks, particularly in the middle of the plug—indicating possible misfires. However, the P0087 code suggests a fuel system issue rather than ignition-related problems. Any insights or troubleshooting steps for this specific P0087 code on a 2012 Hyundai Sonata would be greatly appreciated.