Unable to find any theme or add plugins in WordPress: An unexpected error occurred. Something may be wrong with WordPress.org or this server’s configuration

Symptoms

• While trying to find a theme in WordPress at Domains > example.com > Log in to the  WordPress admin panel > Appearance > Themes or in Domains > example.com > Log in to the  WordPress admin panel > Plugins > Add New, the following error appears: 

  An unexpected error occurred. Something may be wrong with WordPress.org or this server’s configuration. If you continue to have problems, please try the support forums

• If themes are searched in Domains > example.com > WordPress > Themes, nothing is shown in the results:

   

• The following error is shown in the WordPress admin panel in Domains > example.com > Log in to WordPress: 

  Warning: An unexpected error occurred. Something may be wrong with WordPress.org or this server’s configuration. If you continue to have problems, please try the support forums. (WordPress could not establish a secure connection to WordPress.org. Please contact your server administrator.) in /var/www/vhosts/example.com/httpdocs/wp-includes/update.php on line 530

•  The server retrieves correct IP address of the domain api.wordpress.org: 

  # dig +short api.wordpress.org
  198.143.164.251

Cause

Unclear.

Resolution

1. Connect to the server via SSH;
2. Run this command to add api.wordpress.org to the /etc/hosts file: 

   # echo “198.143.164.251 api.wordpress.org” >> /etc/hosts