Customers are currently reporting that the legacy UPS Ready quotes integration within BigCommerce is currently failing due to updates with the UPS api. While some customers are still using this legacy integration, the newer UPS® Real Time Shipping Quotes integration is available and is not having any issues.
If you are currently experiencing issues with the legacy UPS Ready integration, please see this article on how to switch to the new UPS® Real Time Shipping Quotes on your store: https://support.bigcommerce.com/articles/Public/UPS