A little problem with a GET request in PHP - php

Question

I have created a simple registration/login system with PHP/SQL in MVC pattern.
It works perfectly but I noticed a little bug; when I login with user and email that they are not in my database, I can't never visualize the warning message "These user and email are not in our database". I noticed that in the http bar on the top I visualize the GET request "action="error" ONLY when then I refresh the page, and not when I immediately click the submit button for the fields control. Where is the problem?
Here my login page code:
<h2>Login</h2>
<?php
$login = new MvcTemplate();
$login -> loginUserController();
if(isset($_GET['action'])){
if($_GET['action'] == 'error'){
echo '<div class="alert alert-warning">Ops, these user and email are not in our database!</div>';
}
if($_GET['action'] == 'captchafail'){
echo '<div class="alert alert-warning">Ops, flag the Captcha!</div>';
}
}
?>
<form method="POST">
<div class="mb-3">
<label for="exampleInputEmail1" class="form-label">Email</label>
<input type="email" class="form-control" id="exampleInputEmail1" aria-describedby="emailHelp" placeholder="La tua Mail" name="mail" required>
</div>
<div class="mb-3">
<label for="exampleInputPassword1" class="form-label">Password</label>
<input type="password" class="form-control" id="exampleInputPassword1" placeholder="La tua Password" name="password" required>
</div>
<div class="g-recaptcha my-5" data-sitekey="6LdJAwodAAAAALA5PrlYI9n96h5f4AmSab7SOSKC"></div>
<div class="d-grid">
<button type="submit" class="btn btn-primary" name="login">Entra</button>
</div>
</form>
Here the managing of the Login feature in the Controller:
// Gestione della funzione di Login;
public function loginUserController(){
if(isset($_POST['login'])){
// Cifratura della password mediante funzione "crypt";
$securePass = crypt($_POST['password'], '$5$zyPltHmiO9ZqMg7JHRWktNhB_GZ0jiQWvDe0c4N7$');
$dataController = array(
'mail' => $_POST['mail'],
'password' => $securePass
);
$responseDb = Data::loginUserModel($dataController, 'users');
// Controllo di ReCaptcha;
$secret = '6LdJAwodAAAAAOlQKWxeJ2LCydsRpl1M9SrsXqOZ';
$response = $_POST['g-recaptcha-response'];
$remoteIP = $_SERVER['REMOTE_ADDR'];
$verify = file_get_contents("https://www.google.com/recaptcha/api/siteverify?secret=$secret&response=$response&remoteip=$remoteIP");
$result = json_decode($verify);
if($result -> success){
if($responseDb['email'] == $_POST['mail'] && $responseDb['pass'] == $securePass){
// Inizializzo una sessione;
session_start();
// Creo una variabile di sessione;
$_SESSION['validation'] = true;
header('location:users');
}
}elseif(empty($_POST['g-recaptcha-response'])){
header('location:captchafail');
}
else{
header('location:error');
}
}
}
And here the page links.php in the Model directory:
<?php
class Pages{
public static function showPages($links){
if( $links == 'login' ||
$links == 'users' ||
$links == 'update' ||
$links == 'logout'
){
$moduleNav = 'views/modules/'.$links.'.php';
}elseif($links == 'index'){
$moduleNav = 'views/modules/register.php';
}elseif($links == 'ok'){
$moduleNav = 'views/modules/register.php';
}elseif($links == 'error'){
$moduleNav = 'views/modules/login.php';
}elseif($links == 'captchafail'){
$moduleNav = 'views/modules/login.php';
}elseif($links == 'edit'){
$moduleNav = 'views/modules/users.php';
}else{
$moduleNav = 'views/modules/register.php';
}
return $moduleNav;
}
}