Stripe Express Checkout

Added

• New Variable::EVENT_MODIFY_BUTTON_OPTIONS event (ModifyButtonOptionsEvent), fired before the express checkout buttons are rendered. Handlers can modify the options passed to the client side StripeExpressCheckout.init() call.
• The client side element now forwards a paymentMethodConfiguration option (if set) to stripe.elements(), so host projects can control which payment methods the Express Checkout Element displays (set it via EVENT_MODIFY_BUTTON_OPTIONS).

Added

• The express checkout request now flags itself via Craft::$app->params['stripeExpressCheckout'] before processing payment. Host projects can read this flag (e.g. in an EVENT_BUILD_GATEWAY_REQUEST handler) to distinguish the express checkout flow from the regular onsite checkout, since both run through PaymentIntents::createPaymentIntent.

Fixed

• README: corrected setItemQty parameter order to (qty, id?) to match the actual JS signature. Previously documented as (id, qty).

Fixed

• Order is now created with the correct orderSiteId matching the site the customer placed the order from. Previously fell back to the first site in the store.

Added

• siteId is sent with every plugin API request so the order site is deterministic regardless of the AJAX site-resolution.