A Grayscale Shaders does not work on Android?

i hope that you can help me... I have a Shaders for Grayscale Texture ,on PC it working fine,but it never working on any android devices.just like the Shaders load failed.This is my code:

 Shader "Custom/Greyscale" {
      Properties {
          _MainTex ("Base (RGB)", 2D) = "white" {}
      }
      SubShader {
          Tags { "RenderType"="Opaque" }
          LOD 200
          
          CGPROGRAM
          #pragma surface surf Lambert
  
          sampler2D _MainTex;
  
          struct Input {
              float2 uv_MainTex;
          };
  
          void surf (Input IN, inout SurfaceOutput o) {
            
              // Get the original texture colour
              half4 tex = tex2D (_MainTex, IN.uv_MainTex);
              
              // Get the apparent brightness
              half brightness = dot(tex.rgb, half3(1, 1.1, 1));
  
              // Set RGB values equal to brightness
              o.Albedo = brightness;
          }
          ENDCG
          
          
      } 
      FallBack "Diffuse"
  }