What is the deprecated function causing the fatal error in the login.php file?

The fatal error in the login.php file is likely caused by a deprecated function that is no longer supported in the PHP version being used. To solve this issue, you need to replace the deprecated function with a supported alternative. This can be done by identifying the deprecated function in the code and finding a suitable replacement for it.

// Replace the deprecated function with a supported alternative
// Deprecated function: mysql_connect()
// Supported alternative: mysqli_connect()

// Before
$conn = mysql_connect($servername, $username, $password);

// After
$conn = mysqli_connect($servername, $username, $password);