WIX API integrations with delivery carrier

I’m trying to integrate one local carrier in the delivery option WIX has, but I’m having hard time.
The carrier provided me the attached API to start with, but looking at the documentation here I just do not know where to start from. Any advise where to start from? I do not need the whole integration, but only the part where you check the price for the delivery.

Look at using either Wix fetch or Wix HTTP Functions.

https://www.wix.com/corvid/reference/wix-fetch.html
https://support.wix.com/en/article/corvid-accessing-third-party-services-with-the-fetch-api

https://www.wix.com/corvid/reference/wix-http-functions.html
https://support.wix.com/en/article/corvid-exposing-a-site-api-with-http-functions

Corvid example here.
https://www.wix.com/corvid/forum/corvid-tips-and-updates/example-myapi-and-myapiclient