Fix (the worst way) troubles with untrusted certificates in ClassicPress.

fix.php

<?php
/**
 * Plugin Name: twk
 *
 * Description: Fix (the worst way) troubles with untrusted certificates in ClassicPress.
 *
 */

if (!defined('ABSPATH')){
	die('-1');
};

add_filter('http_request_args', 'xsx_fix_ssl_issues', 10, 2 );

function xsx_fix_ssl_issues($r, $url) {

	// Array of regex of sources to fix.
	$fix_domains = [
		'/^https?:\/\/api-v1\.classicpress\.net/',
		'/^https?:\/\/software.gieffeedizioni.it/',
	];

	foreach ($fix_domains as $fix_domain) {
		if(preg_match($fix_domain, $url) === 1) {
			$r['sslverify'] = false;
			return $r;
		}
	}

	return $r;

}