Problem after changing PHP versio 5.6 to 8.2

Hi, i got this java code

 $('#gonder').click(function(){
 var plaka_degiskeni = $('#plaka').val();
 var sifre_degiskeni = $('#sifre').val();
 $.ajax({ 
 type:'POST', 
 url:'sonuc.php',
 data: { plaka: plaka_degiskeni, sifre: sifre_degiskeni },
 success:function(cevap){
 $("#sonuc").html(cevap); 
 }
 });
 });

and i got this sonuc.php code

<?php
header("Content-Type: text/html; charset=Windows-1254");
mysql_connect("localhost","***","***");
mysql_select_db("***");
mysql_query("SET NAMES 'latin5'"); 
$plaka=iconv("UTF-8", "ISO-8859-9",$_POST['plaka']);
$plaka=str_replace(" ","",$plaka);
$sifre=iconv("UTF-8", "ISO-8859-9",$_POST['sifre']);
$sifre=str_replace(" ","",$sifre);
if ($sifre == "***"){
$sorgu = mysql_query("SELECT * FROM Sayfa1 WHERE PLAKA LIKE '$plaka'");
}else{
$sorgu = mysql_query("SELECT * FROM Sayfa1 WHERE PLAKA LIKE '$plaka' AND KAYIT LIKE '$sifre'");
}
$veri=0;
while($r=mysql_fetch_array($sorgu))
{    
    $veri++;
    $servis=$r["SERVIS"];
    $dosya=$r["DOSYA"];
    $durum=$r["DURUM"];
    $plaka=$r["PLAKA"];
    $sigorta=$r["SIGORTA"];
    $kargo=$r["KARGO"];
    $kargo=str_replace("\n",'<br>',$kargo);
?> 
<table> 
<tr> 
<td width="30%"> 
<?php 
    echo "<b>PLAKA</b> <td>$plaka";
?> 
</td> 
</tr> 
<tr> 
<td> 
<?php 
    echo "<b>DOSYA NO</b><td> $dosya";
?> 
</td> 
</tr>
<tr> 
<td> 
<?php
    echo "<b>DOSYA DURUMU</b><td> $durum"; 
?> 
</td> 
</tr> 
<tr> 
<td> 
<?php
    echo "<b>SYGORTA TYRKETY</b><td> $sigorta"; 
?> 
</td> 
</tr> 
<tr> 
<td> 
<?php 
    echo "<b>SERVYS</b><td> $servis";
?> 
</td> 
</tr> 
<tr> 
<td> 
<?php 
    echo "<b>DOSYA NOTU</b><td>$kargo";
?> 
</td> 
</tr> 
<td> 
</td> 
</table> 
<?php
}
if ($veri==0){

function test_input($data) {
    $data = trim($data);
    $data = stripslashes($data);
    $data = htmlspecialchars($data);
    return $data;
  }
 

if (empty($_POST["plaka"])) {
?>    
<table> 
<tr> 
<td width="30%">
<?php    
    echo "<b>PLAKA ALANI ZORUNLUDUR</b>";
?>
</td> 
</tr> 
<td>
</td> 
</table> 
<?php
  } else {
      
    if (empty($_POST["sifre"])) {
?>
<table> 
<tr> 
<td width="30%">
<?php
    echo "<b>TYFRE ALANI ZORUNLUDUR</b>";
?>
</td> 
</tr> 
<td> 
</td> 
</table> 
<?php    
  } else {
?>
<table> 
<tr> 
<td width="30%">
<?php      
      echo "<b>PLAKA YADA TYFRE HATALIDIR</b>";
?>
</td> 
</tr> 
<td>
</td> 
</table> 
<?php    
  }
  }
}
 
?>

Its working fine on php ver.5.6 but when I change php to 8.2 it`s not working anymore…?

What to change in this code to make it run on php 8.2 ? Im sorry but I’m not a programmer. Thanks for any help

The page I need help with: [log in to see the link]