WM_INPUT does not receive mouse updates

Question

Outside of the main, I define a mouse event handler as

int xPosAbsolute = 0;
int yPosAbsolute = 0;
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam)
{
    switch (msg)
    {
        case WM_INPUT:
        {
            UINT dwSize = sizeof(RAWINPUT);
            static BYTE lpb[sizeof(RAWINPUT)];
            GetRawInputData((HRAWINPUT)lparam, RID_INPUT, lpb, &dwSize, sizeof(RAWINPUTHEADER));
            RAWINPUT* raw = (RAWINPUT*)lpb;
            if (raw->header.dwType == RIM_TYPEMOUSE)
            {
                xPosAbsolute += raw->data.mouse.lLastX;
                yPosAbsolute += raw->data.mouse.lLastY;
            }
            return 0;
        }
    }
    return DefWindowProc(hwnd, msg, wparam, lparam);
}

inside of the main I then register and bind the mouse readings as

POINT p;
if (GetCursorPos(&p))
{
    xPosAbsolute = p.x; 
    yPosAbsolute = p.y;
}
RAWINPUTDEVICE Rid[1];
Rid[0].usUsagePage = HID_USAGE_PAGE_GENERIC;
Rid[0].usUsage = HID_USAGE_GENERIC_MOUSE;
Rid[0].dwFlags = RIDEV_INPUTSINK;
Rid[0].hwndTarget = hWnd;
RegisterRawInputDevices(Rid, 1, sizeof(Rid[0]));

Unfortunately, even if I move the mouse, the variables xPosAbsolute and yPosAbsolute never change their values from the initial GetCursorPos setting. Am I missing something in order to make the WndProc work?

EDIT:

Borrowing some of the ingredients from this link, I've included the following in the main

HMODULE hInstance = GetModuleHandle(NULL);
static TCHAR szWindowClass[] = _T("win32app");
WNDCLASSEX wcex;
wcex.cbSize = sizeof(WNDCLASSEX);
wcex.style          = CS_HREDRAW | CS_VREDRAW;
wcex.lpfnWndProc    = WndProc;
wcex.cbClsExtra     = 0;
wcex.cbWndExtra     = 0;
wcex.hInstance      = hInstance;
wcex.hIcon          = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_APPLICATION));
wcex.hCursor        = LoadCursor(NULL, IDC_ARROW);
wcex.hbrBackground  = (HBRUSH)(COLOR_WINDOW+1);
wcex.lpszMenuName   = NULL;
wcex.lpszClassName  = szWindowClass;
wcex.hIconSm        = LoadIcon(wcex.hInstance, 
MAKEINTRESOURCE(IDI_APPLICATION));

RegisterClassEx(&wcex);

to attempt to register WndProc with the window. Unfortunately, this did not give any improvement.