Is this use of nested if else statements considered bad practice? [closed]

I am creating a password reset system for my project. I currently have an password reset link sent to the user's email address and I'm now working on the create-password.php page. I have a selector and validator token to authorise the change of an account's password. In my code, I take these tokens from the url and go through some validation and if there are no errors, a form to change their password is shown, otherwise the corresponding error message is displayed. I use nested if else statements but I have read that this can be bad coding practice for readability and maintenance. I believe that my code is readable but I can understand why someone might find it hard to understand with the combination of HTML and php code, so I would appreciate some insight from someone more experienced whether this is considered bad practice and what could be done alternatively.

<!-- Generic HTML Code -->

<?php

// if there are empty tokens, inform user
if (empty($_GET["selector"]) || empty($_GET["validator"])) {
?>

<!-- Corresponding HTML code for empty token(s) -->

<?php

} else {
    $selector = $_GET["selector"];
    $validator = $_GET["validator"];

    // Checks to see if the variables are legit hexadecimal tokens
    if (ctype_xdigit($selector) !== false && ctype_xdigit($validator) !== false) {
        // Run through database to check if selector and validator token exist for a user and not expired
        if ( not valid selector token|| not valid validator token || expired) {
?>

<!-- Corresponding HTML code for expired link or not valid token(s) -->

<?php

        } else {
?>

<!-- HTML form to change password -->

<?php
        }
    } else {
?>

<!-- Corresponding HTML error message for false hexadecimal token(s) -->

<?php

}
?>