how to pass php variable to charge create in stripe

Question

I have successfully integrated stripe payment. However, when I pass hardcoded amount and currency it works fine, but as I use variable in the charge array it gives me HTTP ERROR 500

My code:

 <?php
require_once "config.php";
session_start();
$depoamount=$_SESSION['stripeamount'];
$curr=$_SESSION['curr'];
$token  = $_POST['stripeToken'];
$email  = $_POST['stripeEmail'];
$custid=$_SESSION['reg_no'];
//$custid='123';
$id=$_POST['ID'];
/* $depoamount=1200;
$curr='inr';*/
$customer = \Stripe\Customer::create([
  'email' => $email,
  'source'  => $token,
  'customer'=> $custid,

]);

$charge = \Stripe\Charge::create([
  'customer' => $customer->id,
  'amount'   => $depoamount,// If I use '5000' it works
  'currency' => $curr,// same if I put 'usd' it works
 ]);

  echo '<h1>Successfully charged</h1>';
  echo $charge->email;
  echo $charge->id;
  echo $custid;
 ?>

I think syntax is ok , however its not working.