Are you integrating with Shopify, Shipping company, or both?
For Shopify, they have an API that you can work with:
Shopify API reference docs[
^]
As for the shipping company, there is not enough information to work with. However, at a guess, you could use the ShipStation API:
Integrating with ShipStation[
^] ... they connect with most of the common carriers:
ShipStation Partner Marketplace[
^]