if ( empty( $request_payment_method ) ) {
			if ( $requires_payment_method ) {
				throw new RouteException(
					'woocommerce_rest_checkout_missing_payment_method',
					esc_html__( 'No payment method provided.', 'woocommerce' ),
					400
				);
			}
			return null;
		}

		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 ) {
		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.
			$this->order->set_customer_id( $customer_id );
			$this->order->save();

			// 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( $this->order );
		wc_log_order_step( '[Store API #6::process_customer] Synced customer data from order', array( 'customer_id' => $this->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;
	}

	/**
	 * 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
			);
		}
	}
}