curl_init() function not working

You need to install CURL support for php.

In Ubuntu you can install it via

sudo apt-get install php5-curl

If you're using apt-get then you won't need to edit any PHP configuration, but you will need to restart your Apache.

sudo /etc/init.d/apache2 restart

If you're still getting issues, then try and use phpinfo() to make sure that CURL is listed as installed. (If it isn't, then you may need to open another question, asking why your packages aren't installing.)

There is an installation manual in the PHP CURL documentation.

For Windows, if anybody is interested, uncomment the following line (by removing the ;) from php.ini

;extension=php_curl.dll

Restart apache server.

I got it working in ubuntu 16.04 by following steps.My php version was 7.0

sudo apt-get install php7.0-curl

sudo service apache2 restart

i got it from this link check here for more details