Nicki Minaj -- Floyd Mayweather Jr. Paid Her $50,000 to Show Up at Daughter's B-Day

Nicki Minaj doesn't even have to sing to make bank -- sources tell TMZ Floyd Mayweather Jr. paid her $50,000 just to show her face at his daughter's 14th birthday party.

According to sources, Mayweather rented out the entire MGM ballroom in Vegas to celebrate Iyanna Mayweather's birthday last weekend -- and Nicki showed up to surprise her.

We're told Nicki stayed for about an hour -- hanging out with Iyanna, taking pics ... annnd that's pretty much it.

You'll recall, Iyanna's birthday party is essentially what set off the brawl between T.I. and Floyd -- after T.I.'s wife Tiny posted a photo of herself with Iyanna. Tiny was an unpaid guest.

Iyanna's pretty spoiled as far as celeb guests go -- last year, Justin Bieber showed up at her party. Just imagine what her sweet 16 will look like.