How to use #extension with GLSL shader

I receive this error when my shader is compiled on Android: Adreno : ERROR: 0:20: '' : GLSL compile error: Extension directives must occur before any non-preprocessor tokens.

My shader looks like:

 Shader "testShader" { // defines the name of the shader
     Properties{
         _MainTex("Texture", 2D) = "" {}
     }
    SubShader { // Unity chooses the subshader that fits the GPU best
       Pass { // some shaders require multiple passes
          GLSLPROGRAM // here begins the part in Unity's GLSL
  
         #extension GL_OES_EGL_image_external : require
          #ifdef VERTEX // here begins the vertex shader
         varying vec2 glFragment_uv;
  
          void main() // all vertex shaders define a main() function
          {
             gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
             glFragment_uv = gl_MultiTexCoord0.xy;
          }
  
          #endif // here ends the definition of the vertex shader
  
  
          #ifdef FRAGMENT // here begins the fragment shader
         varying vec2 glFragment_uv;
         uniform samplerExternalOES _MainTex;
  
          void main() // all fragment shaders define a main() function
          {
             gl_FragColor = texture2D(glFragment_uv, _MainTex);
          }
  
          #endif // here ends the definition of the fragment shader
  
          ENDGLSL // here ends the part in GLSL
       }
    }
 }

The extension is compiled to be after preprocessor tokens