If you see the error above after trying to activate your license key on the license settings page, this means that your server could not connect to https://www.mapsmarker.com for the license validation.
Please ask your hoster for help here. There might be special security precautions preventing your server from communicating directly with https://www.mapsmarker.com (GET requests, Port 443)
It could also be that your server only allows direct connection through a proxy (you can verify this if you are not receiving any WordPress core or plugin updates). If this is the case, the proxy server has to be configured in wp-config.php (please ask your hoster for details about your proxy):
define('WP_PROXY_HOST', '192.168.xx.xxx'); define('WP_PROXY_PORT', '8080'); define('WP_PROXY_USERNAME', 'my_user_name'); define('WP_PROXY_PASSWORD', 'my_password'); define('WP_PROXY_BYPASS_HOSTS', 'localhost, www.example.com');
If that also does not help, please open a support ticket and we will be glad to help you solving your issue!