create this line at the begin of the shader, so you get error messages with line numbers. (without quotation marks)
"#line 2"

undefine variables: define it. par example iResolution and iMouse.
vec3 iResolution = iWorldScale.xyz;
vec2 iMouse = vec2(0);
or
vec3 iMouse = vec3(0);

create the function getSkyboxColor() and call mainImage():
vec3 getSkyboxColor()
{
    vec3 rayDirection = normalize(_normal);
    vec2 position = rayDirection.xy;
    position += 0.5;
    position.y = 1.0 - position.y;
    //position.y = 0 + position.y; //180° turn
    vec4 result;
    mainImage(result, position * iWorldScale.xy);
    return result.xyz;
}