The download for CSFML 2.3 (Visual C++/GCC 64-bit) contains 32-bit libraries, so 64-bit FFIs won't link. Sorry if this is old-hat and I've missed any reasoning for this.
I know I (and others) can just download the source and build ourselves, but I figured since the link is there it was just an oversight if there's anyone running the site who could quickly rebuild 64-bit versions and upload them? Currently, to download prebuilt, 64-bit libs, it looks like 2.2 is the latest version.
Cheers!