Fragment Shader not showing in ThreeJS

I am new to threejs and implementing shaders in it. I brought a fun shader in but I am having issues with displaying it. I believe it is related to the variable “len” in the code but I am not sure. Here is the link to the codepen https://codepen.io/Yerbs/pen/eYWgevO.Any Help would be appreciated
This is the frag shader

fragmentShader: `
uniform vec2 resolution;
uniform float time;

const int AMOUNT = 12;
         
        void main() {
    vec2 coord = 20.0 * (gl_FragCoord.xy - resolution / 2.0) / min(resolution.y, resolution.x);

    float len;

    for (int i = 0; i < AMOUNT; i++){
        len = length(vec2(coord.x, coord.y));

        coord.x = coord.x - cos(coord.y + sin(len)) + cos(time / 9.0);
        coord.y = coord.y + sin(coord.x + cos(len)) + sin(time / 12.0);
    }

    gl_FragColor = vec4(cos(len * 2.0), cos(len * 3.0), cos(len * 1.0), 1.0);
        }
      `
    });

I have tested out previous code so I know it is related to the fragment itself.