Floyd Mayweather says he made over a billion bucks in earnings over his legendary career, but the 50-0 fighter claims all the money didn’t make it to his bank account … and now he’s suing Showtime, claiming they played a big role in his ex-manager screwing him out of hundreds of millions of dollars!

In the lawsuit, filed by Floyd in California, and obtained by TMZ Sports … Mayweather says he’s gunning to “recover hundreds of millions of dollars in the misappropriated funds and damages resulting from a long-running and elaborate scheme of financial fraud,” allegedly perpetrated by his longtime advisor Al Haymon … and now he’s claiming Haymon got “substantial participation and aid” from Showtime and former Showtime Sports president, Stephen Espinoza.

Showtime and Espinoza are listed as defendants … while Haymon is NOT being sued.

Floyd claims Haymon, with whom he worked for over a decade, misappropriated a “significant portion of his career earnings” to the tune of a whopping $340 million … and he says he did so with the help of Showtime and SE.

Mayweather says the money is still “‘missing’ and unaccounted for.”

In the suit, Mayweather references several of his biggest fights, including against Manny Pacquiaoand Conor McGregor, alleging Showtime and Espinoza effectively delivered money owed to Floyd directly into Haymon’s hands by sending accounts essentially controlled by Haymon.

Years later, after the undefeated boxer switched managers and his new team asked to see Showtime’s books, which Floyd claims the network told him were “lost in a flood,” or weren’t accessible.

Mayweather is suing Showtime and Espinoza for aiding and abetting breach of fiduciary duty, civil conspiracy to commit fraud, conversion, and unjust enrichment.

In addition to the $340 million, Mayweather is also seeking punitive damages.