Cannot install Plesk license key, WordPress plugin or a Plesk extension: cURL cannot communicate with license server

Symptoms

• Plesk interface is slow. Time to First byte (TTFB) when loading some Plesk pages is very big but server resources are fine.

• License, WordPress plugin or Plesk extension installation fails with one of the following errors:

  Error: cURL cannot communicate with license server https://id-00.kaid.plesk.com:5224/ (): Couldn't connect to server(7)
  cURL cannot communicate with license server https://id-00.kaid.plesk.com:5224/ (): Couldn't resolve host name(6)

  cURL cannot communicate with license server https://id-00.kaid.plesk.com:443/ (195.214.233.82): SSL connect error(35) cURL cannot communicate with license server https://id-00.kaid.plesk.com:443/ (): Couldn't resolve host name(6) (Error code: 2)

  Error: No properly formed ip addresses

  Error: The license key is invalid. In order to use Plesk, you need to obtain and install a new valid license key. Your license key has expired. To continue using your Plesk, you must purchase a non-expiring commercial license key. Error: cURL cannot communicate with license server https://id-00.kaid.swsoft.com:5224/ (): Failed to connect to id-00.kaid.swsoft.com port 5224: Bad access(7) cURL cannot communicate with license server https://id-00.kaid.swsoft.com:5224/ (): Could not resolve host: id-00.kaid.swsoft.com(6)

  ERR [panel] KeyUpdate Result additional information: cURL verbose output: * Trying 195.214.233.80... * connect to 195.214.233.80 port 5224 failed: Bad access * Failed to connect to ka.plesk.com port 5224: Bad access * Closing connection 0

  cURL cannot communicate with license server https://ka.plesk.com/xmlrpc(): Failed to connect to ka.plesk.com port 443: Timed out(7)
  cURL cannot communicate with license server https://ka.plesk.com/xmlrpc(): Could not resolve host: ka.plesk.com(6)

• One of the following symptoms is true:

  • Cannot connect to ka.plesk.com using telnet utility:

    # telnet ka.plesk.com 443
    Trying 195.214.233.80...
    telnet: Unable to connect to remote host: Connection refused

    OR

    # telnet ka.plesk.com 443
    Trying 195.214.233.80...
    telnet: connect to address 195.214.233.80: Connection timed out
    Trying 195.214.233.81...
    telnet: connect to address 195.214.233.81: Connection timed out
    Trying 195.214.233.82...
    telnet: connect to address 195.214.233.82: Connection timed out

  • cURL HTTPS request fails with:

    # curl --insecure https://ka.plesk.com:443
    curl: (35) TCP connection reset by peer

  • # curl https://ka.plesk.com:443 -v
    ...
    * Connected to ka.plesk.com (195.214.233.81) port 443 (#0)
    ...
    * Cipher selection: ALL:!EXPORT:!EXPORT40:!EXPORT56:!aNULL:!LOW:!RC4:@STRENGTH
    ...
    * TLSv1.2 (OUT), TLS handshake, Client hello (1):
    * Unknown SSL protocol error in connection to ka.plesk.com:443
    ...
    curl: (35) Unknown SSL protocol error in connection to ka.plesk.com:443

  • Or:

    PS > New-Object System.Net.Sockets.TcpClient("ka.plesk.com", 443)
    Client : System.Net.Sockets.Socket
    Available : 0
    Connected : False

Cause

Outgoing connections to the Key Administration server are blocked by a local or intermediate firewall.

Resolution