Can't get plugin to pull data from file

I am working on a plugin that consists of 3 files; the main plugin file, compression_results.php and form.php.

The main file will grab data (using cURL) from one of the other two files, depending on whether there is data in a particular variable or not. The problem is that it currently won’t load the data. I’ve also tried using get_file_contents but it gave me an error saying the file didn’t exist.

I navigated to the url where the file is, and it displayed, so I know it’s there and accessible. I know I can hard-code the contents of the two files into the plugin and be done with it, but I was hoping to make it easier to modify by using three files vs. one.

Any ideas what’s wrong?

<?php
/*
Plugin Name: CSS Compressor
Plugin URI: https://URI_Of_Page_Describing_Plugin_and_Updates
Description: A brief description of the Plugin.
Version: The Plugin's Version Number, e.g.: 1.0
Author: Wildfire Marketing Group
Author URI: https://URI_Of_The_Plugin_Author
License: A "Slug" license name e.g. GPL2
*/

function css_compressor() {

if (isset($_POST["css"])) {

	$old_css_size = strlen($_POST["css"]);
	$css = preg_replace('!/\*[^*]*\*+([^/][^*]*\*+)*/!', '', $_POST["css"]);
	$un_comp = array("" , "    ", "    ", "\r\n", "\n", "\r", "\t", "\\", ";}", "000000", "FFFFFF", "ffffff", "CCCCCC", "cccccc", "999999", "666666", "333333", "0px");
	$comp = array("", "", "", "", "", "", "", "", "}", "000", "FFF", "fff", "CCC", "ccc", "999", "666", "333", "0");
	$css = strip_tags(str_replace($un_comp, $comp, $css));
	$new_css_size = strlen($css);
	$savings = number_format($old_css_size - $new_css_size);
	$percent = round((($old_css_size - $new_css_size) / $old_css_size) * 100);

	$repvar = array('{old_css_size}', '{new_css_size}', '{savings}', '{percent}', '{css}');
	$repval = array($old_css_size, $new_css_size, $savings, $percent, $css);

	$ch = curl_init();
	curl_setopt ($ch, CURLOPT_URL, 'compression-results.php');
	curl_setopt ($ch, CURLOPT_USERAGENT, $user_agent);
	curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1);
	curl_setopt ($ch, CURLOPT_FOLLOWLOCATION, 1);
	curl_setopt ($ch, CURLOPT_TIMEOUT, $timeout);
	$compression_results = curl_exec($ch);
	curl_close($ch);

	$compression_results = str_replace($repvar,$repval,$compression_results);

	echo $compression_results;
}

else

	$ch = curl_init();
	curl_setopt ($ch, CURLOPT_URL, 'form.php');
	curl_setopt ($ch, CURLOPT_USERAGENT, $user_agent);
	curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1);
	curl_setopt ($ch, CURLOPT_FOLLOWLOCATION, 1);
	curl_setopt ($ch, CURLOPT_TIMEOUT, $timeout);
	$form = curl_exec($ch);
	curl_close($ch);

	echo $form;
}

add_shortcode('csscompressor', 'css_compressor');

?>