Ben kullanıcı kontrol etmek için iki yol vardır:

1.if user input (Amount field < 5(user credit):
   do update database the remain amount in my database table.
2.if user input(Amount field) > 5(user credit):
  Do paypal transaction with the submit form.



 <form action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post" id="payPalForm">        
    <input type="hidden" name="item_number" value="01 - General Payment to FreelanceSwitch.com">
    <input name="item_name" type="hidden" id="item_name"  size="45" value="Posting job">    
    <input type="hidden" name="cmd" value="_xclick">    
    <input type="hidden" name="no_note" value="1">    
    <input type="hidden" name="business" value="seller_1265789181_biz@xxx.xxx.xx">    
    <input type="hidden" name="currency_code" value="USD">    
    <input type="hidden" name="return" value="http://freelanceswitch.com/payment-complete/">       
    Paying Page:<input name="amount" type="text" id="amount" size="5">   
    <input type="submit" name="Submit" value="Pay">            
    </form>

Herkes nasıl paypal koşulları formu göndermek ile yapmak bana söyleyebilirdi.?

teşekkürler.

Donny Kurnia @ teşekkürler, şimdi ben denedim:

EDIT ::

function compare_user_credit($paying_price, $user_credit){

    $db = &JFactory::getDBO();
    $user =& JFactory::getUser();
    $user_id = $user->get('id');

    if ($paying_price <= $user_credit) {        
        $remain_credit = $user_credit - $paying_price;
        //DO UPDATE:enough credit
        update_user_credit_after_paying($remain_credit,$user_id);
        $action_after_paying = header("Location: index.php?xxxx=5");
     }
    # Case2 direct to paypal with the submit form.
    else if ($paying_price > $user_credit){
       //Need submit form to paypal.
       $action_after_paying = header("Location: index.php=xxxx&paypal=".$_POST["amount"]);
    }
    return $action_after_paying;
}
$output = '<form method="POST" > ';
     $output .='<h1>Credit:'.get_credit().'</h1>';
     $output .= ' Paying Page <input type="text" name="amount" size=3 max_length=5 />';
     $output .='<input type="submit" name="pay" value="pay" />' ;
     echo $output;

if(isset($_POST["pay"])){
    compare_user_credit($_POST["amount"], $user_credit);

}

HOw Ben Durumunda 02 Paypal ile yapabilirdi. (Paypal ile formu göndermek için doğrudan.)