Parse error: syntax error

The objective is to add past month's payments to payment history table, refresh payment table at end of month for tenants who have paid and advance datedue 1 month,
code:

<?php
$servername = "localhost";
$username = "root";
$password = " ";
$dbname = "homedb";

try {
$conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
  // set the PDO error mode to exception
  $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
  $sql = "INSERT INTO payhist (tenant,unit,amtpaid,amtdue.datedue,prevbal,latechg,secdep,damage,
courtcost,nsf,hudpay,datepaid,comments,phone,cell)
  VALUES ('$tenant','$unit','$amtpaid','$amtdue','$datedue','$prevbal','$latechg','$secdep','$damage',
'$courtcost','$nsf','$hudpay','$datepaid','$comments','$phone','$cell')";
  // use exec() because no results are returned
  $conn->exec($sql);
  echo "New record created successfully";
} catch(PDOException $e) {
echo $sql . "<br>" . $e->getMessage();
}

$conn = null;

$due='due';
$tenant='tenant';
$unit='unit';
$amtdue = (int)'amtdue';
$amtpaid = (int)'amtpaid';
$datedue='datedue';
$prevbal = (int)"prevbal";
$latechg = (int)'latechg';
$secdep = (int)'secdep';
$damage = (int)'damage';
$courtcost = (int)'courtcost';
$nsf = (int)'nsf';
$hudpay = (int)'hudpay';
$phone = 'phone';
$cell = 'cell';

//MySqli Select Query
$sql = "select * FROM paytbl";
$result = mysqli_query($conn,$sql);
if (!$result) {
  printf("Error: %s\n", mysqli_error($conn));
  exit();
}else{
   $results = array();
   while($row = mysqli_fetch_array($result)){
     $results[] = $row;
   }

$due = $amtdue + $prevbal + $latechg + $secdep + $damage + $courtcost + $nsf - $hudpay;

// if datepaid > duedate (datediff), = latechg
{ $latechg = $latechg + 35.00; }

// if no payment or partial payment, add $35 to latechg field and amount not paid to prevbal field
if ($amtpaid < $due)
{ $latechg = $latechg + 35.00; $prevbal = $due - $amtpaid;  }


// if payment = amtdue clear due
if ($amtpaid == $due)
{ $prevbal = 0.00; $latechg = 0.00; }

// if over-payment subtract over-payment from prevbal field
if ($amtpaid > $due)
{ $prevbal = $amtpaid  - $amtdue;  $latechg = 0.00;}  

// refresh every record - give every record the below values
$amtpaid = 0.00; $secdep = 0.00; $damage = 0.00; $courtcost = 0.00; $nsf = 0.00;
$hudpay = 0.00; $datepaid = ' '; $comments = ' ';


$sql = "UPDATE paytbl SET
amtpaid = '$amtpaid', datedue = DATE_ADD(datedue, INTERVAL 1 month ),
secdep = '$secdep', damage = '$damage', courtcost = '$courtcost', nsf = '$nsf',
hudpay = $hudpay, datepaid = '$datepaid', comments = '$comments' WHERE amtpaid >0"; {
  if(mysqli_query($conn, $sql)){ echo "records were updated successfully."; }
else { echo "ERROR: unable to execute $sql. " . mysqli_error($conn); }
  }
    }
  ?>

PHP:

result:
Parse error: syntax error, unexpected '$conn' (T_VARIABLE) in C:\xampp\htdocs\property\refresh2.php on line 8