Required field in a form - php

Question

i have a simple form and i need that some fields are required.
I do not understand why they do not work. In fact, if I click on the Send button, it takes me to an error page.
I have tried inserting both the required = "required" and only required.
How can I do according to you?
Thank you for your time and availability.
<h3> Dati Prenotazione</h3>
 Inserire i dati richiesti:<br><br>
<form method="post" action="input.php">
<b> Richiedente Conferenza:</b><br><br>
 Nominativo:<br> <input type="text" name="nominativo" placeholder="Nome Cognome" size="20" required="required"><br>
 Email: <br>  <input type="email" name="email" size="20" placeholder="email" required><br>
 Oggetto Conferenza:<br> <textarea name="oggetto" rows="5" cols="40" placeholder="Specificare oggetto Videoconferenza" required></textarea><br>
 Data: <br> <input type="date" name="data" required ><br>
 Orario Inizio: <br> <input type="time" name="orario_inizio" min="09:30:00" max="16:30:00" required ><br>
 Orario Fine: <br> <input type="time" name="orario_fine" min="10:00:00" max="18:30:00" required><br>
<br>
<b> Partecipanti Interni </b>
<br>
<br>
<div id="interni">
<div id="first">
 Nominativo:<br> <textarea name="nominativoi" rows="5" cols="30" placeholder="Nome Cognome;" required ></textarea><br>
 Email:<br>  <textarea name="emaili" rows="5" cols="30" placeholder="Inserire Email" required></textarea><br>
input.php
require ('config.php');
// Richiedente
$nominativo = $_POST['nominativo'];
$email = $_POST['email'];
$oggetto = $_POST['oggetto'];
$data = $_POST['data'];
$orario_inizio = $_POST['orario_inizio'];
$orario_fine = $_POST['orario_fine'];
$stanza = 0;
// Personale Interno
$nominativoi = $_POST['nominativoi'];
$emaili = $_POST['emaili'];
// Persona Esterno
$nominativoe = $_POST['nominativoe'];
$emaile = $_POST['emaile'];
//aggiunta di un'ora ( per tornare indietro cambiare $newTimeEnd con $orario_fine
$dateTime = DateTime::createFromFormat('H:i', $orario_fine);
$dateInterval = DateInterval::createFromDateString('1 hour');
$dateTime->add($dateInterval);
$query1 = "INSERT INTO prenotazione (nominativo,email,data,orario_inizio,orario_fine,oggetto,nominativoi,emaili,nominativoe,emaile,stanza) VALUES ('$nominativo','$email','$data','$orario_inizio','$newTimeEnd','$oggetto','$nominativoi','$emaili','$nominativoe','$emaile',1)";
$result1 = $dbh->prepare($query1);
$result1->execute();
$rex = 1;
}
else if ($prenotato == 1 AND $prenotatoaccettato == 0 ){
$query1 = "INSERT INTO prenotazione (nominativo,email,data,orario_inizio,orario_fine,oggetto,nominativoi,emaili,nominativoe,emaile,stanza) VALUES ('$nominativo','$email','$data','$orario_inizio','$newTimeEnd','$oggetto','$nominativoi','$emaili','$nominativoe','$emaile',2)";
$result1 = $dbh->prepare($query1);
$result1->execute();
$rex = 1;
}
EDIT.
When i click submit the error is
Fatal error: Uncaught Error: Call to a member function add() on boolean
( about $dateTime->add($dateInterval); )

Answer 1

check required fields in your code
if (empty($_POST["nominativo"])) {
addError('nominativo','nominativo error text');
} else {
$nominativo = $_POST["nominativo"];
}
Nome Cognome : <input type="text" name="nominativo">
<span class="error">* <?php echo $nominativoErr;?></span>

Answer 2

Isn't you problem rather in the input.php (can you post it ?) ? Are you sure of the path ?
Also, don't trust what is sent, make a validation in your php too, the HTML and JS code can be changed by the user.

Answer 3

you can try something like:
if($email==NULL|$data==NULL) {
?>
<script>
alert("Missing Fields!");
location.href="form1.html";// page where ir your form
</script>
<?php
}
if (!preg_match("/^[a-zA-Z0-9_\.\-]+#[a-zA-Z0-9\-]+\.[a-zA-Z0-9\-\.]+$/", $email)) {
exit('The email format is incorrect.');
}