Sources with direct knowledge of Jay and Kanye's business relationship tell TMZ, the $20 million was a payout advance which could also cover expenses -- including the floating stage -- for Kanye's "Saint Pablo Tour." The money is sometimes used to cover various production costs and staff.

It's actually standard for artists at Kanye's level to get such an advance. It's part of the deal.

Jay certainly made it sound like he and Roc Nation gifted Kanye the dough. In the song, "Kill Jay Z" Jay raps ...

"But you got hurt because you did cool by 'Ye // You gave him 20 million without blinkin' // He gave you 20 minutes on stage, f*** was he thinkin'? // 'F*** wrong with everybody?' is what you sayin' // But if everybody's crazy, you're the one that's insane."

We broke the story ... Kanye bailed on Jay-Z's streaming service, Tidal, over a money dispute. Kanye's decision to leave had nothing to do with the $20 mil. He claims he's owed unrelated millions for subscription bonuses and music video expenses.

Jay has threatened to sue Kanye if he make an exclusive deal with another streaming service, but we're told Kanye's done with exclusive deals.

Jay and 'Ye were once like brothers, and they still are ... Cain and Abel.