Da Brat is already made a dent in paying off her massive $6.4 million debt ... $400 down, $6,399,600 to go.

The rapper performed Saturday night at a bar in Atlanta ... and according to Dennis Byron -- the guy who shot the video -- Brat's raps were inspired by her prison stint.

We broke the story ... Brat has to pay an Atlanta Falcons cheerleader $6.4 million for beating her face in with a bottle back in '07.

We're told Da Brat actually got paid around $2,500 for the gig.

See also

Da Brat's Bottle Victim -- The $6.4 MILLION Injuries ... Gnarly Bloody Gashed Face [PHOTOS]

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