What is the main issue with the PHP function "eintrag" in the provided script?

The main issue with the PHP function "eintrag" in the provided script is that it is not defined within the script. To solve this issue, the function "eintrag" needs to be properly defined before it is called in the script. This can be done by creating a function named "eintrag" with the necessary functionality.

<?php
// Define the function "eintrag"
function eintrag($name, $email, $message) {
    // Add code here to process the entry
}

// Call the function "eintrag" with appropriate parameters
eintrag($name, $email, $message);
?>