Why does writing to this vector throws me an exception?

I'm a 13 year old who is trying to use vectors in C++ properly for the first time. Although when I write to that vector, I get thrown an exception (segmentation fault). I think it means I'm writing to a illegal memory address or illegally writing to that address?

 #include <iostream>
 #include <vector> 
 #include <fstream>
 #include <string>
    
    
        std::vector<std::string>setup_file_contents_vec{};
        std::ifstream setup_file_required_scan{ "exposcan.txt" };    
        std::string buffer;
        while(setup_file_required_scan >> buffer) { setup_file_contents_vec.push_back(buffer); }
        std::vector <std::string> user_details_confirmation(3);
        for (int i = 0; i < 4; i++){ std::cout << " "; }
        std::cout << " Login details 1/3\n\n";
        for (int i = 0; i < 6; i++){ std::cout << " "; }
        std::cout << "First Name : ";
        std::cin >> user_details_confirmation[0];
        if(user_details_confirmation[0] != setup_file_contents_vec[0]) {/* code */}