HELP ME FIND THIS ACTION MANHWA

So it's Korean action supernatural manhwa. I don't remember much except that our MC was a high school student who did part time as some smuggler and when he enter the otherworld to retrieve that item he mets a girl whose there on her school test or something. And apparently the girl is some rich chaebol so she promises he'll get compensated if he helps her out. They deal with this gorilla like monster too. He basically saves her and she said she'll repay that debt or something. What I do remember is the place some underground old subway(?) Where MC would have his illegal dealing there was an old ajusshi who basically gets/talks the client and first, these obviously insult MC when they find out he's the one that going saying he's a brat what can he do. PLEASE HELP IT'S BEEN BUGGING ME FOR DAYS I WANNA KNOW WHICH MANHWA IS THIS!! ╥﹏╥