What is the potential issue with the disappearing error message in the PHP form?

The potential issue with the disappearing error message in the PHP form is that it may not be displayed to the user if the page reloads after submitting the form. To solve this issue, you can store the error message in a session variable before redirecting the user back to the form page. Then, you can check if the session variable is set and display the error message accordingly. 

<?php
session_start();

// Check form submission
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // Validate form data
    if (empty($_POST["username"])) {
        $_SESSION["error_message"] = "Username is required.";
        header("Location: form.php");
        exit;
    }
}

// Display error message if set
if (isset($_SESSION["error_message"])) {
    echo $_SESSION["error_message"];
    unset($_SESSION["error_message"]);
}
?>

Keywords

PHP form error message validation session.

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