e when the Store API checkout draft order is first materialised.
			 *
			 * Use this hook for first-touch logic that should only run when the draft
			 * order is initially created (e.g. analytics, abandoned-cart trackers). As
			 * of WooCommerce 10.8.0 the Store API defers draft order creation to
			 * place-order time, so this action fires once at POST rather than on the
			 * first PATCH.
			 *
			 * @since 10.8.0
			 *
			 * @param \WC_Order $order Order object.
			 */
			do_action( 'woocommerce_store_api_checkout_order_created', $this->order );
		} else {
			$this->order_controller->update_order_from_cart( $this->order, true );
			wc_log_order_step( '[Store API #4::create_or_update_draft_order] Updated order from cart', array( 'order_object' => $this->order ) );
		}

		wc_do_deprecated_action(
			'__experimental_woocommerce_blocks_checkout_update_order_meta',
			array(
				$this->order,
			),
			'6.3.0',
			'woocommerce_store_api_checkout_update_order_meta',
			'This action was deprecated in WooCommerce Blocks version 6.3.0. Please use woocommerce_store_api_checkout_update_order_meta instead.'
		);

		wc_do_deprecated_action(
			'woocommerce_blocks_checkout_update_order_meta',
			array(
				$this->order,
			),
			'7.2.0',
			'woocommerce_store_api_checkout_update_order_meta',
			'This action was deprecated in WooCommerce Blocks version 7.2.0. Please use woocommerce_store_api_checkout_update_order_meta instead.'
		);

		/**
		 * Fires when the Checkout Block/Store API updates an order's meta data.
		 *
		 * This hook gives extensions the chance to add or update meta data on the $order.
		 * Throwing an exception from a callback attached to this action will make the Checkout Block render in a warning state, effectively preventing checkout.
		 *
		 * This is similar to existing core hook woocommerce_checkout_update_order_meta.
		 * We're using a new action:
		 * - To keep the interface focused (only pass $order, not passing request data).
		 * - This also explicitly indicates these orders are from checkout block/StoreAPI.
		 *
		 * @since 7.2.0
		 *
		 * @see https://github.com/woocommerce/woocommerce-gutenberg-products-block/pull/3686
		 *
		 * @param \WC_Order $order Order object.
		 */
		do_action( 'woocommerce_store_api_checkout_update_order_meta', $this->order );

		// Confirm order is valid before proceeding further.
		if ( ! $this->order instanceof \WC_Order ) {
			throw new RouteException(
				'woocommerce_rest_checkout_missing_order',
				esc_html__( 'Unable to create order', 'woocommerce' ),
				500
			);
		}

		// Store order ID to session.
		$this->set_draft_order_id( $this->order->get_id() );
		wc_log_order_step( '[Store API #4::create_or_update_draft_order] Set order draft id', array( 'order_object' => $this->order ) );
	}

	/**
	 * Updates a customer address field.
	 *
	 * @param \WC_Customer $customer The customer to update.
	 * @param string       $key The key of the field to update.
	 * @param mixed        $value The value to update the field to.
	 * @param string       $address_type The type of address to update (billing|shipping).
	 */
	private function update_customer_address_field( $customer, $key, $value, $address_type ) {
		$callback = "set_{$address_type}_{$key}";

		if ( is_callable( [ $customer, $callback ] ) ) {
			$customer->$callback( $value );
			return;
		}

		if ( $this->additional_fields_controller->is_field( $key ) ) {
			$this->additional_fields_controller->persist_field_for_customer( $key, $value, $customer, $address_type );
		}
	}

	/**
	 * Updates the current customer session using data from the request (e.g. address data).
	 *
	 * Address session data is synced to the order itself later on by OrderController::update_order_from_cart()
	 *
	 * @param \WP_REST_Request $request Full details about the request.
	 */
	private function update_customer_from_request( \WP_REST_Request $request ) {
		$customer                  = WC()->customer;
		$additional_field_contexts = [
			'shipping_address' => [
				'group'    => 'shipping',
				'location' => 'address',
				'param'    => 'shipping_address',
			],
			'billing_address'  => [
				'group'    => 'billing',
				'location' => 'address',
				'param'    => 'billing_address',
			],
			'contact'          => [
				'group'    => 'other',
				'location' => 'contact',
				'param'    => 'additional_fields',
			],
		];

		foreach ( $additional_field_contexts as $context => $context_data ) {

			$document_object = $this->get_document_object_from_rest_request( $request );
			$document_object->set_context( $context );
			$additional_fields = $this->additional_fields_controller->get_contextual_fields_for_location( $context_data['location'], $document_object );

			if ( 'shipping_address' === $context_data['param'] ) {
				$field_values = WC()->cart->needs_shipping()
					? (array) ( $request['shipping_address'] ?? $request['billing_address'] ?? [] )
					: (array) ( $request['billing_address'] ?? [] );
			} else {
				$field_values = (array) $request[ $context_data['param'] ] ?? [];
			}

			if ( 'address' === $context_data['location'] ) {
				$persist_keys = array_merge( $this->additional_fields_controller->get_address_fields_keys(), [ 'email' ], array_keys( $additional_fields ) );
			} else {
				$persist_keys = array_keys( $additional_fields );
			}

			foreach ( $field_values as $key => $value ) {
				if ( in_array( $key, $persist_keys, true ) ) {
					$this->update_customer_address_field( $customer, $key, $value, $context_data['group'] );
				}
			}
			wc_log_order_step( '[Store API #3::update_customer_from_request] Persisted ' . $context . ' fields' );
		}

		/**
		 * Fires when the Checkout Block/Store API updates a customer from the API request data.
		 *
		 * @since 8.2.0
		 *
		 * @param \WC_Customer $customer Customer object.
		 * @param \WP_REST_Request $request Full details about the request.
		 */
		do_action( 'woocommerce_store_api_checkout_update_customer_from_request', $customer, $request );

		$customer->save();
	}

	/**
	 * Gets the chosen payment method from the request.
	 *
	 * @throws RouteException On error.
	 * @param \WP_REST_Request $request Request object.
	 * @return \WC_Payment_Gateway|null
	 */
	private function get_request_payment_method( \WP_REST_Request $request ) {
		$request_payment_method = wc_clean( wp_unslash( $request['payment_method'] ?? '' ) );

		if ( empty( $request_payment_method ) ) {
			return null;
		}

		$available_gateways = WC()->payment_gateways->get_available_payment_gateways();

		if ( ! isset( $available_gateways[ $request_payment_method ] ) ) {
			$all_payment_gateways = WC()->payment_gateways->payment_gateways();
			$gateway_title        = isset( $all_payment_gateways[ $request_payment_method ] ) ? $all_payment_gateways[ $request_payment_method ]->get_title() : $request_payment_method;
			throw new RouteException(
				'woocommerce_rest_checkout_payment_method_disabled',
				sprintf(
					// Translators: %s Payment method ID.
					esc_html__( '%s is not available for this order—please choose a different payment method', 'woocommerce' ),
					esc_html( $gateway_title )
				),
				400
			);
		}

		return $available_gateways[ $request_payment_method ];
	}

	/**
	 * Order processing relating to customer account.
	 *
	 * Creates a customer account as needed (based on request & store settings) and  updates the order with the new customer ID.
	 * Updates the order with user details (e.g. address).
	 *
	 * @throws RouteException API error object with error details.
	 * @param \WP_REST_Request $request Request object.
	 */
	private function process_customer( \WP_REST_Request $request ) {
		$order = $this->get_order_or_throw();

		if ( $this->should_create_customer_account( $request ) ) {
			$customer_id = wc_create_new_customer(
				$request['billing_address']['email'],
				'',
				$request['customer_password'],
				[
					'first_name' => $request['billing_address']['first_name'],
					'last_name'  => $request['billing_address']['last_name'],
					'source'     => 'store-api',
				]
			);

			if ( is_wp_error( $customer_id ) ) {
				throw new RouteException(
					esc_html( $customer_id->get_error_code() ),
					esc_html( $customer_id->get_error_message() ),
					400
				);
			}

			// Associate customer with the order.
			$order->set_customer_id( $customer_id );

			// Set the customer auth cookie.
			wc_set_customer_auth_cookie( $customer_id );
			wc_log_order_step( '[Store API #6::process_customer] Created new customer', array( 'customer_id' => $customer_id ) );
		}

		// Persist customer address data to account.
		$this->order_controller->sync_customer_data_with_order( $order );
		wc_log_order_step( '[Store API #6::process_customer] Synced customer data from order', array( 'customer_id' => $order->get_customer_id() ) );
	}

	/**
	 * Check request options and store (shop) config to determine if a user account should be created as part of order
	 * processing.
	 *
	 * @param \WP_REST_Request $request The current request object being handled.
	 * @return boolean True if a new user account should be created.
	 */
	private function should_create_customer_account( \WP_REST_Request $request ) {
		if ( is_user_logged_in() ) {
			return false;
		}

		// Return false if registration is not enabled for the store.
		if ( false === filter_var( WC()->checkout()->is_registration_enabled(), FILTER_VALIDATE_BOOLEAN ) ) {
			return false;
		}

		// Return true if the store requires an account for all purchases. Note - checkbox is not displayed to shopper in this case.
		if ( true === filter_var( WC()->checkout()->is_registration_required(), FILTER_VALIDATE_BOOLEAN ) ) {
			return true;
		}

		// Create an account if requested via the endpoint.
		if ( true === filter_var( $request['create_account'], FILTER_VALIDATE_BOOLEAN ) ) {
			// User has requested an account as part of checkout processing.
			return true;
		}

		return false;
	}

	/**
	 * Reject the order if what the customer is going to be charged at is higher from what they saw.
	 *
	 * Runs on POST /checkout only, before the draft order is materialised, so a mismatch leaves
	 * no order behind. The check only runs when the client sends the total it displayed; flows
	 * that cannot know the final total up front (e.g. some express payment methods) omit it and
	 * are unaffected.
	 *
	 * @phpstan-param \WP_REST_Request<array<string, mixed>> $request
	 *
	 * @param \WP_REST_Request $request Request object.
	 * @throws RouteException When the recalculated total is higher. Returns HTTP 409 with the refreshed cart so the client can display the updated total.
	 */
	private function validate_order_totals( \WP_REST_Request $request ): void {
		// The route schema constrains this to minor-unit digits, so the integer comparison below is exact.
		$expected_total = (string) ( $request['expected_total'] ?? '' );

		if ( '' === $expected_total ) {
			return;
		}

		// CartSchema::prepare_money_response() is not exported, so we use the money formatter directly here to match the total_price format.
		$decimals     = wc_get_price_decimals();
		$actual_total = woocommerce_store_api_get_formatter( 'money' )->format(
			$this->cart_controller->get_cart_instance()->get_total( 'edit' ),
			[ 'decimals' => $decimals ]
		);

		if ( (int) $actual_total <= (int) $expected_total ) {
			return;
		}

		$expected_amount = wc_remove_number_precision( absint( $expected_total ) );
		$actual_amount   = wc_remove_number_precision( absint( $actual_total ) );

		throw new RouteException(
			'woocommerce_rest_checkout_total_mismatch',
			sprintf(
				/* translators: %1$s: total the shopper confirmed, %2$s: updated, higher total */
				esc_html__( 'The order total changed from %1$s to %2$s while you were checking out. Please review the updated total and place your order again.', 'woocommerce' ),
				esc_html( wc_price( $expected_amount, [ 'in_span' => false ] ) ),
				esc_html( wc_price( $actual_amount, [ 'in_span' => false ] ) )
			),
			409,
			[
				'expected_total' => absint( $expected_total ),
				'actual_total'   => absint( $actual_total ),
			]
		);
	}

	/**
	 * This validates if the order can be placed regarding settings in WooCommerce > Settings > Accounts & Privacy
	 * If registration during checkout is disabled, guest checkout is disabled and the user is not logged in, prevent checkout.
	 *
	 * @throws RouteException If user cannot place order.
	 */
	private function validate_user_can_place_order() {
		if (
			// "woocommerce_enable_signup_and_login_from_checkout" === no.
			false === filter_var( WC()->checkout()->is_registration_enabled(), FILTER_VALIDATE_BOOLEAN ) &&
			// "woocommerce_enable_guest_checkout" === no.
			true === filter_var( WC()->checkout()->is_registration_required(), FILTER_VALIDATE_BOOLEAN ) &&
			! is_user_logged_in()
		) {
			throw new RouteException(
				'woocommerce_rest_guest_checkout_disabled',
				esc_html(
					/**
					 * Filter to customize the checkout message when a user must be logged in.
					 *
					 * @since 9.4.3
					 *
					 * @param string $message Message to display when a user must be logged in to check out.
					 */
					apply_filters(
						'woocommerce_checkout_must_be_logged_in_message',
						__( 'You must be logged in to checkout.', 'woocommerce' )
					)
				),
				403
			);
		}
	}
}