Cardi B's Thrown Microphone's $100k eBay Offer Falls Through

The nearly six-figure transaction for the microphone Cardi B chucked into her crowd, sparking a police investigation, has hit a snag ... we're told the winning bidder didn't pay up.

Here's the deal ... Cardi's infamous microphone was being auctioned on eBay and the bidding war came to an end Tuesday with a $99,900 winning bid ... or so it seemed.

Scott Fisher, the mic owner running the auction, tells TMZ … unfortunately, his suspicions came true and the winning bidder failed to pay for Cardi's mic.

We're told the person who placed the winning bid had 48 hours to fork over the cash, but didn't respond to multiple messages ... so Scott still has the mic. The proceeds from the auction were supposed to benefit charity, and Scott says he's exploring his options ... including sending a purchase offer to the second-highest bidder.

LM Cases, a case company in Ohio, heard about the story and hooked him up with a mic case for whoever ends up with it.

Scott says if the other top bidder doesn't end up buying the mic, he's considering selling it privately.

There's quite a story behind the mic ... as we reported, Cardi was performing at Drai's Beachclub in Las Vegas when she asked the crowd to splash her with water, only to get pissed when someone later tossed ice and liquid on her, resulting in the mic toss.