Shopify employs a server side shipping cache.
What this means, is when you submit an order/address at checkout to fetch rates, Shopify caches the rates that are returned on their servers for about a day. So if the exact same order is submitted ( identical products and identical address ) again within 24 hours, instead of asking the app for new rates, it just show whatever rate it has in the cache.
This can be annoying when testing rates at checkout while configuring the app. It's likely that while testing you will see a rate at checkout and then perhaps adjust the rate, or add a rule to the rate, or add a rate. If you go back to the checkout after making an update and just reload the page, your changes will not appear.
How to bust the shipping cache
The shipping cache will be busted and your updated rates will show if you....
Change some piece of the shipping address you are testing with
Change which products are in the cart
Change the quantity of product in the cart
The easiest way to bust the cache is to increment the street number of the shipping address.
100 Broadway, New York, NY 10006
101 Broadway, New York, NY 10006
102 Broadway, New York, NY 10006
103 Broadway, New York, NY 10006
What will not bust the shipping cache
Refreshing the browser window on the checkout page
Opening an incognito/private browser window
Clearing your browser cookies, cache
Changing the First or Last name
Because the cache is on Shopify servers ( a server side cache ), it has nothing to do with your browser, it has to do with Shopify seeing an identical order ( products and address )
How you can tell if you busted the cache
You can tell you busted the cache if you see, even if briefly, a little spinner icon on the shipping rates page.
If you don't see the little spinner, and the rates immediately appear, then it means the shipping cache has not been busted.
You'll also know you've busted the cache when the changes you've made appear.
Next in Getting Started
Getting Started with Advanced Shipping Rules
Before you Start
Testing Rates and Going Live
Bust the shipping cache when testing