Unable to activate license in SolusVM 2

Symptoms

1. Unable to activate a license in SolusVM 2 - empty pop up or SVM_ERROR: "The license is invalid: the token has expired" 
   shown in SolusVM 2 > Licensing

2. In web server log the following error is shown:

   # docker service logs solus_nginx | grep error
   [error] 697#697: *154 FastCGI sent in stderr: "PHP message: [2020-02-26 08:45:02] production.ERROR: cURL error 6: Could not resolve host: ka.plesk.com (see http://curl.haxx.se/libcurl/c/libcurl-errors.html) {"userId":2,"exception":"[object] (GuzzleHttp\\Exception\\ConnectException(code: 0): cURL error 6: Could not resolve host: ka.plesk.com (see http://curl.haxx.se/libcurl/c/libcurl-errors.html) at /var/www/backend/vendor/guzzlehttp/guzzle/src/Handler/CurlFactory.php:185)

3. iptables is empty or missing docker rules:

   # iptables -L | grep -i docker

Cause

Missing docker rules in iptables that forward traffic to SolusVM 2 containers.

Resolution

1. Access SolusVM 2 master server over SSH.

2. Recreate iptables rules by restarting Docker service:

   # systemctl restart docker