How to remove error Call to undefined function curl_init()?

Problem: Call to undefined function curl_init()?

Solution: This error occurs when cURL library is not installed on your system or enabled in your PHP installation.
In order to resolve this error, install cURL library.

1. For Linux – Terminal Command :

   sudo apt-get install php-curl

2. For Windows:
   Download cURL library from Official Website
   Go to your php.ini file and remove the ; mark from the beginning of the following line:

   ;extension=php_curl.dll

Reference: http://php.net/manual/en/curl.installation.php