Coupon Codes and eCart6

I've added a coupon code form to my cart page and everything works correctly as far as applying the correct discount when the correct discount code is entered. What I can't do is validate if a correct coupon code is entered. How can I validate when someone enters a coupon code if it is a valid coupon code and if it isn't valid display a message not a valid coupon code?

you would need to hand code this:

<?php
if(isset($_POST['CouponCode']) {
  if($_POST['CouponCode'] != "ValidCode") { 
    $_SESSION['badCoupon'] = "yes";
  } else {
    $_SESSION['badCoupon'] = "no";
  }
}
?>

then to show the error:

<?php if(isset($_SESSION['badCoupon']) && $_SESSION['badCoupon'] == "yes")) echo "you entered an incorrect coupon code"; ?>

Lets say that I have 3 valid coupon codes: 1.airflight 2.facebook 3.pinterest How should the top portion of the code be written?

if(($_POST['CouponCode'] != "airflight") || ($_POST['CouponCode'] != "facebook") || ($_POST['CouponCode'] != "pinterest")) {

I can't seem to get it to work can you take a look at the code and tell me what I'm doing wrong?

you have the code inside a validatonb show if:

<?php
if (ValidatedField('cart','cart')) {
if ((strpos((",".ValidatedField("cart","cart").","), "," . "1" . ",") !== false || "1" == "")) {
if (!(false)) {
?>
<?php
if(isset($_POST['Coupon_Code'])) {
if(($_POST['Coupon_Code'] != "airflight") || ($_POST['Coupon_Code'] != "facebook") || ($_POST['Coupon_Code'] != "pinterest")) {
$_SESSION['badCoupon'] = "yes";
} else {
$_SESSION['badCoupon'] = "no";
}
}
?>
<?php if(isset($_SESSION['badCoupon']) && ($_SESSION['badCoupon'] == "yes")) echo "you entered an incorrect coupon code"; ?>
<span class="serverInvalidState" id="Coupon_Code_ServerError">Please enter valid coupon code</span>
<?php //WAFV_Conditional cart.php cart(1:)
}
}
}?>

it needs to be outside of the validation show if.

Moved it outside and I'm getting closer but whether you out in a valid code or invalid it says the coupon code is invalid. Here is the code:
<?php
if(isset($_POST['Coupon_Code'])) {
if(($_POST['Coupon_Code'] != "airflight") || ($_POST['Coupon_Code'] != "facebook") || ($_POST['Coupon_Code'] != "pinterest")) {
$_SESSION['badCoupon'] = "yes"; }
else {
$_SESSION['badCoupon'] = "no";
}
}
?>

Can't figure out why all coupon codes are invalid.

I'll need to troubleshoot directly, see the private message section.

Here is the requested info

When you compare to only one coupon code everything works fine.

<?php
if(isset($_POST['Coupon_Code'])) {
if($_POST['Coupon_Code'] != "airflight") {
$_SESSION['badCoupon'] = "yes";
} else {
$_SESSION['badCoupon'] = "no";
}
}
?>
This code works fine. Its the code for three coupon codes that isn't working

<?php
if(isset($_POST['Coupon_Code'])) {
if(($_POST['Coupon_Code'] != "airflight") || ($_POST['Coupon_Code'] != "facebook") || ($_POST['Coupon_Code'] != "pinterest")) {
$_SESSION['badCoupon'] = "yes"; }
else {
$_SESSION['badCoupon'] = "no";
}
}
?>