Don't mess with American Express -- that's the lesson for hip-hop mega-producer Sean Garrett, who was just ordered to fork over $108,084 to the credit card company.
TMZ broke the story ... Amex sued Garrett -- who's banged out hits with Beyonce, Usher, and Nicki Minaj -- claiming he never paid off the hefty tab on his card.
Amex filed a motion for default judgment last month -- because Garrett didn't respond to the lawsuit -- and the judge ruled in Amex's favor.
Unfortunately for Amex, Garrett has a ton of other financial woes -- the State of Georgia filed a tax lien against him earlier this year, claiming he owes over $1 MILLION in back taxes for the years 2006, 2007, and 2010.
Garrett previously claimed the AMEX bill was the result of identity theft. He has not responded to our calls for comment.