problem

recurly.php

              $subscription = new Recurly_Subscription();
              $subscription->plan_code = $_POST['plan_id'];
              $subscription->currency = 'USD';

              $unique_id = uniqid();

              $subscription->account = new Recurly_Account($unique_id);
              $subscription->account->first_name = $_POST['user']['first_name'];
              $subscription->account->last_name = $_POST['user']['last_name'];
              $subscription->account->email = $_POST['user']['email'];

              // Now we create a bare BillingInfo with a token
              $subscription->account->billing_info = new Recurly_BillingInfo();
              $subscription->account->billing_info->token_id = $_POST['token'];


              // addons

            if( isset( $_POST['selected'] ) ){


                $addons = $_POST['selected'] ;

                foreach ($addons as $addon) {
                    $addon1 = new Recurly_SubscriptionAddOn();
                    $addon1->add_on_code = $addon['name'];
                    $addon1->quantity = $addon['quantity'];
                    $addon1->unit_amount_in_cents = $addon['amount'];
                    $subscription->subscription_add_ons[] = $addon1;
                    
                }


            }

             // Create the subscription
              $subscription->create();


              if( $_POST['user']['coupon']){

                  $coupon = Recurly_Coupon::get($_POST['user']['coupon']);
                  $redemption = $coupon->redeemCoupon($unique_id , 'USD');


              }

Add at Line 4: $subscription->coupon_code = 'yourCouponCode';