The CSRF token is invalid. Please try to resubmit the form

This error message is typically related to a security feature called "Cross-Site Request Forgery" (CSRF) protection. When a user submits a form on a website, a token is generated and sent with the form data. The server then checks the token to ensure that the form was actually submitted by the user and not by a third-party website. If the token is invalid, the server will return an error message. To resolve this issue, the user should try resubmitting the form and ensure that they are not using any third-party software or browser extensions that may be interfering with the form submission.

In PHP, this error commonly occurs when the session expires, the token is missing, or the submitted value fails validation. Ensure that session_start() is called before checking the token, and use hash_equals() for secure comparison:

session_start();
$submittedToken = $_POST['csrf_token'] ?? '';
$storedToken = $_SESSION['csrf_token'] ?? '';

if (!hash_equals($storedToken, $submittedToken)) {
    // Token mismatch or expired session
    exit('The CSRF token is invalid. Please try to resubmit the form.');
}