12:48 PM PT -- We just got the FULL birthday wish video ... Lil Wayne, Nicki Minaj, Mack Maine, Bow Wow, and DJ Khaled are in it too. Pretty cool.
Justin Bieber now does BIRTHDAYS -- at least for the filthy rich daughters of millionaire rap executives -- and we got video proof ... the Biebs singing for Birdman's little girl at her over-the-top sweet sixteen this weekend.
Bria Williams celebrated the big 1-6 at The Bath Club in Miami Beach Saturday night -- a Paris-themed bash replete with a Bugatti'd out arrival, a "glitter" carpet entrance, a giant cake ... and her big present, a matte black Mercedes G-Class.
But the real highlight -- Bieber sent her a "happy birthday" video ... which was played in the middle of the party.
It's a nice gesture ... but don't count on Bieber sending you one if you're not worth at least $100 million.