Raymarcher | time voxel raymarcher using OpenGL GLSL shaders to perform | Graphics library

I know there are a lot of resources on this, but none of them have worked for me.
Some are: webgl readpixels is always returning 0,0,0,0,
and this one: https://stackoverflow.com/questions/44869599/readpixels-from-webgl-canvas\ as well as this one: Read pixels from a WebGL texture
but none of them have been either helpful or successful.

The goal: Render an offscreen canvas with a WebGL shader, then use that as a texture in a separate WebGL shader.

Notes:

• For these WebGL shaders, I'm using a generic vertex shader used for pixel shaders, specifically, a raytracer/raymarcher. This is: attribute vec2 a_position; void main() { gl_Position = vec4(a_position.xy, 0.0, 1.0); }. This vertex shader is inputted two triangles that cover the screen, so basically the fragment shader is doing all the work.

Problem: In order to get the image data off of the offscreen canvas, I've tried these methods:

1. The WebGL gl.readPixels function