why does this custom shader not work?

i found this shader on a very old post and it was the thing i just needed, sadly i cant get it to work and i dont know why.

 Shader "Global-Mapper" {
     Properties{
         _PeakColor("PeakColor", Color) = (0.8,0.9,0.9,1)
         _PeakLevel("PeakLevel", Float) = 300
         _Level3Color("Level3Color", Color) = (0.75,0.53,0,1)
         _Level3("Level3", Float) = 200
         _Level2Color("Level2Color", Color) = (0.69,0.63,0.31,1)
         _Level2("Level2", Float) = 100
         _Level1Color("Level1Color", Color) = (0.65,0.86,0.63,1)
         _WaterLevel("WaterLevel", Float) = 0
         _WaterColor("WaterColor", Color) = (0.37,0.78,0.92,1)
         _Slope("Slope Fader", Range(0,1)) = 0
     }
         SubShader{
         Tags{ "RenderType" = "Opaque" }
         Fog{ Mode Off }
         Tags{ "LightMode" = "Always" }
         CGPROGRAM
 #pragma surface surf Lambert vertex:vert
     struct Input {
         float3 customColor;
         float3 worldPos;
     };
     void vert(inout appdata_full v, out Input o) {
         UNITY_INITIALIZE_OUTPUT(Input, o);
         o.customColor = abs(v.normal.y);
 
     }
     float _PeakLevel;
     float4 _PeakColor;
     float _Level3;
     float4 _Level3Color;
     float _Level2;
     float4 _Level2Color;
     float _Level1;
     float4 _Level1Color;
     float _Slope;
     float _WaterLevel;
     float4 _WaterColor;
     void surf(Input IN, inout SurfaceOutput o) {
         if (IN.worldPos.y >= _PeakLevel)
             o.Albedo = _PeakColor;
         if (IN.worldPos.y <= _PeakLevel)
             o.Albedo = lerp(_Level3Color, _PeakColor, (IN.worldPos.y - _Level3) / (_PeakLevel - _Level3));
         if (IN.worldPos.y <= _Level3)
             o.Albedo = lerp(_Level2Color, _Level3Color, (IN.worldPos.y - _Level2) / (_Level3 - _Level2));
         if (IN.worldPos.y <= _Level2)
             o.Albedo = lerp(_Level1Color, _Level2Color, (IN.worldPos.y - _WaterLevel) / (_Level2 - _WaterLevel));
         if (IN.worldPos.y <= _WaterLevel)
             o.Albedo = _WaterColor;
         o.Albedo *= saturate(IN.customColor + _Slope);
     }
     ENDCG
     }
         Fallback "Diffuse"
 }

i hope that some1 can help me with this