Obviously, fan fiction cannot be copyrighted or sold because it’s a derivative work of licensed content. I know all of the legal bits regarding the direct profit from the work itself.
But are there any other methods for generating even a little money? Is begging for Patreon or some other tip service the only option?
Well, you could just change all the names and remove all explicit references to the original and then sell it. I was just looking at the new game Tempest Rising, which is extremely obvious about copying the plot and design of Command and Conquer, but it’s been changed just enough to avoid copyright.
The Twilight / Fifty Shades of Grey gambit.