UniVRM shader problem

Making a double sided shader for a VRM model in unity it works in unity but not VSeeFace

VSeeFace


what the code is supposed to do is display a texture on a frontfacing normal then display white on a backface but it just puts out purple I don’t know why the code is just the UNIGLTF but edited
here is the code

Shader "UniGLTF/Special"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _Color ("Main Color", COLOR) = (1,1,1,1)
        _Cutoff ("Alpha Cutoff", Range(0, 1)) = 0.5
        _Test ("Main Color", COLOR) = (1,1,1,1)
        [HideInInspector] _BlendMode ("_BlendMode", Float) = 0.0
        [HideInInspector] _CullMode ("_CullMode", Float) = 2.0
        [HideInInspector] _VColBlendMode ("_VColBlendMode", Float) = 0.0
        [HideInInspector] _SrcBlend ("_SrcBlend", Float) = 1.0
        [HideInInspector] _DstBlend ("_DstBlend", Float) = 0.0
        [HideInInspector] _ZWrite ("_ZWrite", Float) = 1.0

        // VertexColor
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            Cull [_CullMode]
            Blend [_SrcBlend] [_DstBlend]
            ZWrite [_ZWrite]
            ZTest LEqual
            BlendOp Add, Max
            
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile_fog
            #pragma multi_compile _ _ALPHATEST_ON _ALPHABLEND_ON
            #pragma multi_compile _ _VERTEXCOL_MUL
            
            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
            #if defined(_VERTEXCOL_MUL)
                fixed4 color : COLOR;
            #endif
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct v2f
            {
                float4 vertex : SV_POSITION;
                float2 uv : TEXCOORD0;
                UNITY_FOG_COORDS(1)
            #if defined(_VERTEXCOL_MUL)
                fixed4 color : COLOR;
            #endif
                UNITY_VERTEX_OUTPUT_STEREO
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            half4 _Color;
            half _Cutoff;
            
            v2f vert (appdata v)
            {
                v2f o;
                UNITY_SETUP_INSTANCE_ID(v);
                UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                
                UNITY_TRANSFER_FOG(o,o.vertex);
                
            #if defined(_VERTEXCOL_MUL)
                o.color = v.color;
            #endif
                return o;
            }
            
            fixed4 frag (v2f i, float isFrontFace : VFACE) : SV_Target
            {
                if(isFrontFace > 0)
                {
                    fixed4 col = tex2D(_MainTex, i.uv) * _Color;
                    
                    #if defined(_VERTEXCOL_MUL)
                        col *= i.color;
                    #endif
                    
                    #if defined(_ALPHATEST_ON)
                        clip(col.a - _Cutoff);
                    #endif
                    
                    #if !defined(_ALPHATEST_ON) && !defined(_ALPHABLEND_ON)
                        col.a = 1.0;
                    #endif
                    
                    UNITY_APPLY_FOG(i.fogCoord, col);
                    return col;
                }
                else
                {
                    return float4(1.0,1.0,1.0,1.0);
                }
            }
            ENDCG
        }
    }
    CustomEditor "UniGLTF.UniUnlit.UniUnlitEditor"
    Fallback "Unlit/Texture"
}

this what it looks like in unity

does VSeeFace have any log file?
at least usually unity applications would display shader errors there.

not to my knowledge no

if its made in unity, usually there is player.log file
windows %USERPROFILE%\AppData\LocalLow\CompanyName\ProductName\Player.log
check others: