Add missing checkout session params + expand discount data in webhook

[alim888aa]

createCheckoutSession is missing common Stripe Checkout parameters:

allow_promotion_codes
payment_method_types
payment_method_options
discounts
locale
currency

Additionally, the checkout.session.completed webhook handler doesn't expand discount data. When a customer uses a promo code, session.discounts contains IDs, not the actual promotion code string. Custom handlers need to make a separate stripe.checkout.sessions.retrieve() call to get it.

Since processEvent already makes Stripe API calls for subscription mode (retrieving subscriptions/invoices), adding a similar call to expand discounts would be consistent.

[kallaspriit]

As a workaround creating the checkout session using Stripe SDK directly works but supporting these additional parameters would be nice.

const stripeApi = new StripeSDK(stripeSecretKey);

const session = await stripeApi.checkout.sessions.create({
  mode: "subscription",
  line_items: [{ price: priceId, quantity: 1 }],
  customer: customer.customerId,
  success_url: `${billingUrl}?checkout=success`,
  cancel_url: billingUrl,
  allow_promotion_codes: true,
  ...
});

[alim888aa]

Good idea. It's probably best to just have a param that accepts any optional StripeSDK.Checkout.SessionCreateParams. Something like this:

async createCheckoutSession(

  ctx: ActionCtx,

  args: {

    priceId: string;

    customerId?: string;

    mode: "payment" | "subscription" | "setup";

    successUrl: string;

    cancelUrl: string;

    quantity?: number;

    metadata?: Record<string, string>;

    subscriptionMetadata?: Record<string, string>;

    paymentIntentMetadata?: Record<string, string>;

    additionalParams?: Partial<StripeSDK.Checkout.SessionCreateParams>;

  },

)

Usage:

await stripeSubscriptions.createCheckoutSession(ctx, {

  mode: "subscription",

  priceId,

  customerId: customer.customerId,

  successUrl: `${billingUrl}?checkout=success`,

  cancelUrl: billingUrl,

  additionalParams: {

    allow_promotion_codes: true,

  },

});

I'll probably edit my PR accordingly.

[kallaspriit]

Yeah makes sense, can probably re-use typings from Stripe SDK and omit the already handled ones so if new parameters ever get added they'd appear there too.