Questions on third party carrier rates integration

[Lundin]

Hi,
A couple of questions:

• Am i understanding this correctly, that the third party carrier rates integration is working with a webhook URL specified by me to my endpoint so i can return a json response with my calculated shipping rates based on the checkout items in the request (i have on my side api to various transport methods). But then the documentation keep mention the US,CA limitation, what is that all about ? Is that for "plug-n-play" based URLs or am i as a developer in Europe not able to use the callback/webhook method for our store/clients with my "own" calculations ?
  "If your store isn't located in the United States or Canada, then you can't show carrier-calculated rates."
  https://help.shopify.com/en/manual/shipping/setting-up-and-managing-your-shipping/enabling-shipping-...
  
  
• Can we test this feature, carries rates integration, in trial mode by add a credit card and select advanced plan ?
  
  
• Assume i dont want to go the above route, but instead render my own "transport widget" on the checkout page with various options based on the checkout items (js script that post the cart items and render the response in the widget). Is there a way of updating the total price of the checkout on selecting a shipping method ? I have been looking at the rest api and sales channel where one can PUT a shipping rate handle to the checkout id (which i assume then gets re-rendered) but then i need to pre-create every shipping rate in the store ahead? Also can i hide the default shipping methods in checkout that wants to render the created shipping rates profiles in liquid template then ?
  
  Thanks for any insight on this 🙂