7:54 PM PT -- Pump has been released from custody. A source close tells us he was issued a ticket and will not have to appear in court ... it'll be handled by his legal team.

3:42 PM PT -- According to the police report -- obtained by TMZ -- officers initiated the stop after discovering the license plate on Pump's Rolls-Royce actually belonged to a Mini Cooper. When cops asked Pump for a driver's license, he allegedly told them he'd never had one.Lil Pump's been arrested in Miami, and TMZ got pics of him in handcuffs during the bust, and his grinning mug shot after he was taken into custody.

Witnesses tell us the "Drug Addicts" rapper was pulled over Wednesday afternoon while driving a black Rolls-Royce -- and, according to law enforcement, it's because of an issue with his driver's license.

His Miami-Dade County Jail booking sheet says he doesn't have a valid license. He's currently still in custody.

We broke the story ... Pump was also arrested earlier this year for firing a gun into the door of his L.A.-area home. He originally claimed intruders fired from the outside, but cops quickly realized the rapper was the shooter ... and there were no intruders.

Pump was taken to a juvenile detention center because he was 17 at the time. He turned 18 a couple weeks ago.

Happy birthday?