Major Payne is not based on a true story. It's a fictional tale crafted by the imagination of the writers to provide an engaging and comical narrative.
Yes, it probably is. Given the title, especially the 'untold story' part, it seems like it would be a documentary aiming to present facts and details about Sarah Payne's situation that haven't been widely known before.
The real story of Max Payne is one of a tragic hero. He was a cop who lost his family in a brutal crime. Driven by vengeance, he delved into a dark underworld filled with crime and corruption. He fought against powerful and dangerous criminals while also dealing with his own inner demons and the pain of his loss.