insert in sql with mysqli and cookie in php - php

Question

I have two files: Studio.php and Principale.php
In the first one i want insert in my database some values and add them also in a table of Principale.php
With the first row of the table in Principale.php and the first add in the table of my database it works, after no.
I thought to use a for loop to create more rows in the table of Principale.php
It shows me also this error : Notice: Undefined index: titolo1 in C:\xampp\htdocs\Progetto\Principale.php on line 47
I think $res2 return a value different than TRUE but i don't know why.
Code of Principale.php :
$n=$_COOKIE['idstudio'];
for ($i=1;$i<$n;$i++) {
echo "<table style='border: 1px solid black; margin-left:auto; margin-
right:auto;'><caption> <p>Esperienze di Studio</p>
</caption> <thead style='color:green;'> <tr>";
echo "<th style='border: 1px solid black;'> Titolo </th><th
style='border: 1px solid black;'> Anno </th><th style='border: 1px solid
black;'> Luogo </th> ";
echo "</tr> </thead> <tbody style='color:blue'> <tr>";
echo "<td style='border: 1px solid black;'>".$_COOKIE["titolo$i"]."
</td>";
echo "<td style='border: 1px solid black;'>".$_COOKIE["anno$i"]."</td>";
echo "<td style='border: 1px solid black;'>".$_COOKIE["luogo$i"]."
</td>";
echo "</tr></tbody</table><br><br>";
}
echo "</div>";
Code of Studio.php :
$luogo = $_POST["luogo"];
$anno = $_POST["anno"];
$titolo = $_POST["titolo"];
$sql6="SELECT education_experience_id FROM education_experience ORDER BY
education_experience_id DESC LIMIT 1;";
$result2=mysqli_query($connessione,$sql6);
$row2=mysqli_fetch_array($result2,MYSQLI_NUM);
$last_id2=$row2[0];
$id2 = $last_id2+1;
$eeid=$_COOKIE['id'];
$sql9="INSERT into EDUCATION_EXPERIENCE
(education_experience_id,title,year,place,user_id) VALUES
('$id2','$titolo','$anno','$luogo','$eeid')";
$res2=mysqli_query($connessione,$sql9);
echo "<br>";
mysqli_error($connessione);
if($res2 ==TRUE) {
setcookie("luogo$id2", $luogo, strtotime("+1 month"));
setcookie("anno$id2", $anno, strtotime("+1 month"));
setcookie("titolo$id2", $titolo, strtotime("+1 month"));
setcookie("idstudio",$id2,strtotime("+1 month"));
header("Location: Principale.php");
}
else
{
echo "Impossibile aggiungere Esperienza<br>";
echo "<a href='Principale.php'>Clicca Qui</a> per tornare alla pagina
principale.";
}