There's a ton of money at stake when Jake Paul and Tommy Fury enter the ring on Sunday ... 'cause the two boxers just agreed to a hefty bet that could leave one of them without a dime!!
The Problem Child proposed the deal during their pre-fight press conference minutes ago ... saying if TNT wins, he will double his purse -- but if Jake is victorious, he gets EVERYTHING.
The deal was solidified with a handshake ... and Jake said he even had his lawyers draft up the paperwork beforehand to prove he's 100% serious.