Ying Yang Twin -- My Music Career Sucks ... I Can't Afford My Child Support

The Ying Yang Twins haven’t had a hit song in years ... that's why one of the rappers begged a judge to lower his child support payments, and he just got a huge break ... TMZ has learned.

According to docs filed in Georgia, D-Roc -- aka De'Angelo Holmes -- had been paying his ex-wife $2,500 a month in support for their daughter ... an arrangement that was made when he was pulling down more than 19-grand a month.

But the Twins haven’t had a hit since 2005's "Wait (The Whisper Song) --- so D-Roc went back to court ... hat in hand ... and asked for a reduction, claiming he's only making $2,860 a month.

D-Roc hammered out a sweet deal ... 'cause, according to the docs, his child support payments are now just $550 a month -- plus, he got a payment plan for the $45K in back support he owes.

One more reason D-Roc needed a break -- he has 5 other mouths to feed.