Forward declaration of class and still Error: Variable has incomplete type

I have defined two classes : (1) class Point_CCS_xy , and (2) random_Point_CCS_xy_generator. I would like to define a function in Point_CCS_xy class which makes use of random_Point_CCS_xy_generator class to generate random points on a cartesian coordinate system within a range Min and Max, both of which have been defined as long double. I have already forward declared class random_Point_CCS_xy_generator, however I get an Variable has incomplete type random_Point_CCS_xy_generator error on this line random_Point_CCS_xy_generator rpg(Min, Max); and also this error Member reference base type 'vector<Point_CCS_xy> (size_t)' (aka 'vector<Point_CCS_xy> (unsigned long long)') is not a structure or union, on this line Point_CCS_xy_vec.push_back(p);.

MWE

#include<iostream>
#include<fstream>
#include<functional>
#include<algorithm>
#include<vector>
#include<deque>
#include<queue>
#include<set>
#include<list>
#include<limits>
#include<string>
#include<memory>

using namespace std;
typedef long double ld;

class random_Point_CCS_xy_generator;

class Point_CCS_xy{
private:
    long double x_coordinate_ {0.0};
    long double y_coordinate_ {0.0};
public:
    Point_CCS_xy () = default;
    Point_CCS_xy(long double x, long double y): x_coordinate_(x), y_coordinate_(y) {}
    ~Point_CCS_xy() = default;

    // copy constructor through construction delegation method
    Point_CCS_xy(const Point_CCS_xy& cpyObj) : Point_CCS_xy(cpyObj.x_coordinate_, cpyObj.y_coordinate_)
    {

    }



 // Copy and Mover Assignment Operators, 
 // also setters and getters, and a few utility functions come here inlcuding:
friend ostream& operator<<(ostream& os, const Point_CCS_xy& pnt);


// Problematic Function -> source of ERRORS
vector<Point_CCS_xy> Random_Point_CCS_xy(long double Min, long double Max, size_t n) {
        random_Point_CCS_xy_generator rpg(Min, Max);
        vector<Point_CCS_xy> Point_CCS_xy_vec(size_t);
        for (size_t i = 0; i < n; ++i){
            Point_CCS_xy p = Point_CCS_xy(rpg());
            Point_CCS_xy_vec.push_back(p);
        }
        return Point_CCS_xy_vec;
    }
};

ostream& operator<<(ostream& os, const Point_CCS_xy& pnt) {
    os << "X: " << setw(10)<< left << pnt.x_coordinate_ << " Y: " << setw(10)<< left << pnt.y_coordinate_;
    return os;
}

class random_Point_CCS_xy_generator {
public:
    random_Point_CCS_xy_generator(long double min, long double max)
            : engine_(std::random_device()()), distribution_(min, max) {}

    Point_CCS_xy operator()() {
        long double x = distribution_(engine_);
        long double y = distribution_(engine_);
        return Point_CCS_xy(x, y);
    }

    std::mt19937 engine_;
    std::uniform_real_distribution<double> distribution_;
};

As I am a newbie in programming, any idea would be highly appreciated.