when other libraries has json.hpp, #include "json.hpp" can't load nlohmann::json.
i think moving include/json.hpp to include/nlohmann/json.hpp and replace
#include "json.hpp"
to
#include "nlohmann/json.hpp"
or
#include <nlohmann/json.hpp>
for reference:
#include <json.hpp> works sometime.
but i think this is not complete solution, maybe...