CiviCRM has detected that the function
curl_init is not available, and is showing a warning.
phpinfo() will show changes immediately (since PHP is started for each execution), while PHP in the webserver needs you to restart it separately to pick up new PHP modules. (These modes of running PHP also have different configurations loaded per default - but apt should already have enabled
curl for each.)
You can verify this by checking
phpinfo through the webserver (eg in Drupal, visit
admin/reports/status/php; in WordPress you might need to use this phpinfo plugin or just create a
phpinfo file in your site. If you see curl missing there, it could be a reload is all you need.
Depending on your webserver configuration (PHP can run as FPM, mod_php, etc), you'll need to restart the service (eg apache2, php-fpm) which runs PHP on your server. Most likely,
sudo service <your php service> reload