c++ – Geometry Shader must have a max vertex count DirectX 11

I am trying to add a Geometry Shader to my DirectX 11 project in C++

There are no examples of this anywhere I look. There are millions of tutorials on OpenGL but nothing on geometry shaders in DirectX

I just wrote a basic shader below, but I get the following error when trying to build it

error X3514: 'LightGeometryShader' must have a max vertex count

Can anyone please advise on what this shader is missing to be able to compile?

////////////////////////////////////////////////////////////////////////////////
// Filename: light.gs
////////////////////////////////////////////////////////////////////////////////


//////////////
// TYPEDEFS //
//////////////
struct GeometryInputType
{
    float4 position : POSITION;
    float2 tex : TEXCOORD0;
    float3 normal : NORMAL;
};

struct PixelInputType
{
    float4 position : SV_POSITION;
    float2 tex : TEXCOORD0;
    float3 normal : NORMAL;
};


////////////////////////////////////////////////////////////////////////////////
// Geometry Shader
////////////////////////////////////////////////////////////////////////////////
PixelInputType LightGeometryShader(GeometryInputType input)
{
    PixelInputType output;
    
    output = input;

    return output;
}