I'm a Messenger in an Infinite World

One day, a software called [Post Office] appeared on Aicen's phone for no apparent reason, and this software asked her to deliver a letter. She thought it was just an ordinary task, but during the process of delivering the message, she was forcibly pulled into a game - a game hosted by a creature with a goat's head and human body calling itself "Weiyang". Where did the letter that the mysterious force asked her to send come from? Where are you going again? What is the end of each game you participate in? There are constant copies, surrounded by ghosts and monsters. From being forced to join the game, to being successful every step of the way, her only goal—— In this never-ending game, survive until the truth of it all is revealed. Note: 1. I won't rely on props to clear the game, but my writing skills are limited, so I apologize. 2. Not a horror genre