Unresolved external symbol referenced in function main

I've been looking for a fix to this error for a while but idk how to solve it. The thing is im getting this error when trying to compile: Error

Im building the structure of an engine following this series: https://www.youtube.com/watch?v=88dmtleVywk&t=835s

And the error is here:


extern Ocacho::Application* Ocacho::CreateApplication();

int main(int argc, char** argv)
    /*This is not definetly*/
    OG_CORE_LOG_INFO("Initializing Ocacho engine!");

    Ocacho::Application* app = Ocacho::CreateApplication();
    delete app;
    #error Ocacho only support Windows!