PHP on Server downloads empty images - php

Question

I've got a php function that downloads youtube thumbnails to the server, and it works fine on my local version, however as soon as it gets uploaded to the server all of the .jpg files that it downloads are empty.
function download_thumbnail() {
preg_match('/src="(.+?)"/', get_field('youtube_link'), $matches); //Pull the URL of the video out of the iframe generated by ACF
preg_match("/embed\/(.+)\?/", $matches[1], $vid_id); //Pull the ID of the video from the URL
$download_url = "https://img.youtube.com/vi/".$vid_id[1]."/maxresdefault.jpg"; //Use the standard youtube link to get the max res thumbnail
$uploads = wp_upload_dir();
$path = $uploads['path']."/"; //Get the upload path
$filename = $vid_id[1].'.jpg'; //Set the filename as the ID of the video
$save_as = $path.$filename; //Full path of the created file
if(!file_exists($save_as)) { //Check if file exists
$ch = curl_init($download_url); //Initialize the PHP cURL to the youtube page
$fp = fopen($save_as, 'wb'); //Start the path link
curl_setopt($ch, CURLOPT_FILE, $fp); //Download the image to the path link
curl_setopt($ch, CURLOPT_HEADER, 0);
curl_exec($ch);
curl_close($ch);
fclose($fp);
$filetype = wp_check_filetype( basename( $save_as ), null ); //Check the file type
$attachment = array( //Create neccessary wordpress data to the image
'guid' => $uploads['url'] . '/' . basename( $save_as ),
'post_mime_type' => $filetype['type'],
'post_title' => preg_replace( '/\.[^.]+$/', '', basename( $save_as ) ),
'post_content' => '',
'post_status' => 'inherit'
);
$attach_id = wp_insert_attachment( $attachment, $save_as, get_the_ID() ); //Add neccessary wordpress data to the image
require_once( ABSPATH . 'wp-admin/includes/image.php' ); //Make sure that the image gets registered as an image
$attach_data = wp_generate_attachment_metadata( $attach_id, $save_as ); //Generate more meta data
wp_update_attachment_metadata( $attach_id, $attach_data ); //Attatch the meta data
set_post_thumbnail( get_the_ID(), $attach_id ); //Set image as the featured image
}
}
Any help / insight is appreciated.
Thanks