Fix error before M7

packages/api-client/src/resources/commerce.ts

@@ -54,7 +54,17 @@ export interface CommerceResource {
   removeCartLine(locale: Locale, variantId: string, options?: RequestOptions): Promise<Cart>;
 
   getCheckoutQuote(locale: Locale, options?: RequestOptions): Promise<Cart>;
-  placeOrder(locale: Locale, input: PlaceOrderInput, options?: RequestOptions): Promise<Order>;
+  /**
+   * `idempotencyKey` must be stable across retries of the *same* attempt and
+   * different between attempts — the server uses it to tell a resend apart from
+   * a second purchase.
+   */
+  placeOrder(
+    locale: Locale,
+    idempotencyKey: string,
+    input: PlaceOrderInput,
+    options?: RequestOptions,
+  ): Promise<Order>;
   lookupOrder(orderNumber: string, email: string, options?: RequestOptions): Promise<Order>;
   getPlacedOrder(id: string, options?: RequestOptions): Promise<Order>;
 }
@@ -112,8 +122,11 @@ export function createCommerceResource(http: HttpClient): CommerceResource {
     getCheckoutQuote: (locale, options) =>
       http.get<Cart>('/checkout/quote', cartOptions(locale, options)),
 
-    placeOrder: (locale, input, options) =>
-      http.post<Order>('/checkout/orders', input, cartOptions(locale, options)),
+    placeOrder: (locale, idempotencyKey, input, options) =>
+      http.post<Order>('/checkout/orders', input, {
+        ...cartOptions(locale, options),
+        headers: { 'Idempotency-Key': idempotencyKey, ...options?.headers },
+      }),
 
     getPlacedOrder: (id, options) =>
       http.get<Order>(`/checkout/orders/${encodeURIComponent(id)}`, {