title: Stripe Checkout session applies coupon to the one-time fee instead of the subscription
body: <p>I'm following the official <a href="https://stripe.com/docs/payments/checkout/set-up-a-subscription#coupons" rel="nofollow noreferrer">Stripe checkout guide for subscriptions</a>, and specifically trying to have a checkout session for a subscription with the following features:</p>
  <ul>
  <li>14 Free trial</li>
  <li>$1 one-time fee</li>
  <li>Coupon code that applies to the <strong>subscription</strong></li>
  </ul>
  <p>the following code snippet is typescript and creates the checkout session successfully. However when checking out, the coupon applies to the one time fee instead of the subscription.</p>
  <pre><code>            const params: Stripe.Checkout.SessionCreateParams = {
              customer_email: req.body.email,
              payment_method_types: [&quot;card&quot;],
              line_items: [
                  {
                      price: &quot;price_HLcJok7ggz03hn&quot;,
                      quantity: 1,
                  },
                  {
                      price: &quot;price_HLD1Vu4SyAn8uQ&quot;,
                      quantity: 1,
                  },
              ],
              mode: &quot;subscription&quot;,
              subscription_data: {
                  trial_period_days: 14,
                  coupon: req.body.name,
              },
              success_url: `http://localhost:3000/success?session_id={CHECKOUT_SESSION_ID}`,
              cancel_url: `http://localhost:3000/success?session_id={CHECKOUT_SESSION_ID}`,
          }
          const checkoutSession: Stripe.Checkout.Session = await stripe.checkout.sessions.create(
              params
          )
  </code></pre>
  <p>I'm following the Stripe section on adding one time fees, AND the section about adding coupons. It seems silly that the coupon code would only apply to the one time fee and not the subscription. <strong>I'd like to have the coupon work only for the subscription, not the one time fee.</strong>
  <a href="https://stripe.com/docs/payments/checkout/set-up-a-subscription#adding-setup-fee" rel="nofollow noreferrer">https://stripe.com/docs/payments/checkout/set-up-a-subscription#adding-setup-fee</a>
  <a href="https://stripe.com/docs/payments/checkout/set-up-a-subscription#coupons" rel="nofollow noreferrer">https://stripe.com/docs/payments/checkout/set-up-a-subscription#coupons</a></p>
  <p>This is a screenshot of the checkout screen after the redirect from my site to Stripe:
  <a href="https://i.stack.imgur.com/na0ju.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/na0ju.png" alt="enter image description here" /></a></p>