I am sorry for the delayed of this reply, it seems like I still unable to connect with your FTP server, this is my current office IP address 175.138.4.27
By the way, I noticed you have disabled this PHP function curl_multi_exec on your server, can you remove this function from your PHP server under Disabled Functions section and see how it goes?
You have to remove this curl_multi_exec from your PHP server (php.ini) under this Disabled Functions section, you can refer my attached screenshot below.
If the issue still persist, can you add my current IP address 202.188.88.112 into your FTP server whitelist?