I have added and enabled UPS Shipping add-on for Expresso Store, configured all settings but it seems not working in a current (even store_example) checkout flow. Described below how to reproduce that issue.
During the checkout process on the /checkout page there will be no shipping methods available on the drop down. Then I went to "Continue Billing Details", typed all my billing/shipping details and clicked on "Review Order". From the Confirm Order screen I clicked on Back button and then Back again to /checkout page and now I have got Shipping methods available, but when new cart is created Shipping methods are gone again.
Any clue what is going on there? So far now word from Expresso Store dev team on that issue and it is kind of serious stuck for me (shipping comes as 0 each time when customer follow checkout steps).