Earning billions afk fishing

Does AFK-Fishing actually rack in a billion overnight ? if so...how so ? i barely make 20million

EDIT : I am master 8 fishing

EDIT : 780 Mastery, Fishing +5 & Luck +5.

EDIT : After reading all comments, I started building up my mastery through manos accessories, otter backpack, and otter pet for auto-fishing time reduction. I am at mastery 1207 right now, and I earn around 120m, which translates to around 400m after bargaining with the furthest trade manager.

I want to thank you all for sharing your knowledge in this post and helping me accomplish this.