Your sandbox vps was running a proxy server (xray) that served general internet traffic through its public port 8443. Running a proxy or VPN isn’t allowed on the free plan (Terms 2(e)), so we are closing that port. 
Your sandbox and its files are untouched and still running. To run a proxy or VPN, upgrade to a paid plan. 
If you think this is a mistake, reply to this email. 
直接给我发了邮件，免费版不让用代理了给我端口...