This is an accepted solution.
Hank here from Shopify.
Enabling third-party carrier-calculated rates is a huge benefit for your store, enabling you to use more apps, or couriers for your shipping needs.
For those on the Shopify plan or below, this can be activated for a fee of $20USD a month, or if you switch from monthly to yearly billing, you can add the third-party calculated shipping rates feature for free.
As this would be deemed an additional subscription, access to your account is needed. In order to provide you with the most efficient support for account-specific questions related to shipping, please visit our Help Center, log in to your account, and create a support request to connect with one of the live chat teams.
All the best,