What could be causing the "Fatal error: Call to undefined function: session_start()" message in PHP?

The "Fatal error: Call to undefined function: session_start()" message in PHP is likely caused by the session_start() function not being recognized by PHP. This can happen if the PHP session module is not enabled in the php.ini configuration file. To solve this issue, you need to enable the session module in the php.ini file by uncommenting or adding the line extension=php_session.dll (Windows) or extension=session.so (Unix/Linux). Once the session module is enabled, the session_start() function should work properly.

// Enable session module in php.ini configuration file
// Uncomment or add the following line:
// extension=php_session.dll (Windows) or extension=session.so (Unix/Linux)

// Start session
session_start();

// Your PHP code here