SEAN KINGSTONORDERED TO COUGH UP $301Kin Jewelry Lawsuit

Sean Kingston just picked up another L ... and it wasn't cheap.

The rapper's been ordered to pay $301,500 to NYC jeweler Aqua Master who sued him over 9 pieces of jewelry but was never paid. The items included 2 diamond necklaces, a few gold chains, a ring and 2 watches. 

Making matters worse, Aqua says Sean flaunted the pieces on his IG.

TMZ broke the story ... Aqua sued Sean back in 2016, but the rapper never responded to the lawsuit, so the judge issued a default judgment. Aqua says Sean made a halfhearted attempt to pay ... sending 2 checks. But they later bounced.

Sean's got issues with jewelers over the years. He was sued in Florida and had already been ordered to pay another jeweler in 2015.