How to download a ZIP file into the wp-plugins folder programmatically? - wordpress

Question

I am creating a WordPress plugin which should download a ZIP file from a remote location and place it into the wp-plugins folder.
So I created a method which downloads the file using Curl (this works fine) and should then place the file into the wp-plugins folder. I am using the WP_Filesystem in order to make sure I have the rights to place a file on the server. This is what I have until now:
public function download_plugin($url, $path)
{
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$data = curl_exec($ch);
curl_close($ch);
global $wp_filesystem;
if(defined('FS_CHMOD_FILE'))
{
$chmod = FS_CHMOD_FILE;
}
else
{
$chmod = 0755;
}
if (empty($wp_filesystem))
{
require_once (ABSPATH . '/wp-admin/includes/file.php');
WP_Filesystem();
}
if(!$wp_filesystem->put_contents(
$path,
$data,
$chmod
))
else
{
return new \WP_Error('writing_error', 'Error when writing file');
}
}
When I run the method no file is being created on the server. The $path variable however has the right path and the $data variable does contain the ZIP file as a string. The WordPress method put_contents however does nothing. It returns null even when I change the method's parameter to something that should definitely work like $wp_filesystem->put_contents(WP_PLUGIN_DIR.'example.txt','Some text',FS_CHMOD_FILE));.
Is there anything I am doing wrong? It's really difficult to debug since I don't get any errors and put_contents always returns null.