From TheGamer: “Not all of Nier Replicant’s sidequests are mandatory, but if you want to collect all of the weapons and unlock any endings beyond Ending B, you’ll need to complete A Bridge in Peril. This one isn’t nearly as long as quests like The Damaged Map, so it should make for a quick clear, and easy rewards. For completing the quest, you’ll receive 30,000 gold and a new weapon – Labyrinth’s Whisper.”

Source: N4G PC Nier Replicant: A Bridge In Peril Guide