>get_contextual_fields_for_location( 'contact', $document_object );
			$additional_fields         = array_merge( $additional_fields_order, $additional_fields_contact );
		} else {
			$additional_fields_order   = $this->additional_fields_controller->get_fields_for_location( 'order' );
			$additional_fields_contact = $this->additional_fields_controller->get_fields_for_location( 'contact' );
			$additional_fields         = array_merge( $additional_fields_order, $additional_fields_contact );
		}

		$field_values = (array) $request['additional_fields'] ?? [];

		foreach ( $additional_fields as $key => $field ) {
			if ( isset( $field_values[ $key ] ) ) {
				$this->additional_fields_controller->persist_field_for_order( $key, $field_values[ $key ], $this->order, 'other', false );
			}
		}

		// We need to sync the customer additional fields with the order otherwise they will be overwritten on next page load.
		if ( 0 !== $this->order->get_customer_id() && get_current_user_id() === $this->order->get_customer_id() ) {
			$customer = new WC_Customer( $this->order->get_customer_id() );
			$this->additional_fields_controller->sync_customer_additional_fields_with_order(
				$this->order,
				$customer
			);
			$customer->save();
		}
	}

	/**
	 * Returns a document object from a REST request.
	 *
	 * @param \WP_REST_Request $request The REST request.
	 * @return DocumentObject The document object or null if experimental blocks are not enabled.
	 */
	public function get_document_object_from_rest_request( \WP_REST_Request $request ) {
		return new DocumentObject(
			[
				'customer' => [
					'billing_address'   => $request['billing_address'],
					'shipping_address'  => $request['shipping_address'],
					'additional_fields' => array_intersect_key(
						$request['additional_fields'] ?? [],
						array_flip( $this->additional_fields_controller->get_contact_fields_keys() )
					),
				],
				'checkout' => [
					'payment_method'    => $request['payment_method'],
					'create_account'    => $request['create_account'],
					'customer_note'     => $request['customer_note'],
					'additional_fields' => array_intersect_key(
						$request['additional_fields'] ?? [],
						array_flip( $this->additional_fields_controller->get_order_fields_keys() )
					),
				],
			]
		);
	}
}
<br />
<b>Fatal error</b>:  Trait 'Automattic\WooCommerce\StoreApi\Utilities\CheckoutTrait' not found in <b>/home/htzanetatos/public_html/wp-content/plugins/woocommerce/src/StoreApi/Routes/V1/Checkout.php</b> on line <b>17</b><br />