When does the getTransportDetails operation return the CarrierName? Amazon SP-API, FulfillmentInbound

Question

The Amazon MWS API used to return a carrier name after some time, during the cost estimation process. With the Amazon Selling Partner API, I've waited for over 2 hours, and although the report says that the cost has been estimated, I still don't have a carrier name.

When does the carrier name get assigned?

Here is the reference:

https://developer-docs.amazon.com/sp-api/docs/fulfillment-inbound-api-v0-reference#gettransportdetails

I used the SP API to mimic an already existing shipment that had been entered manually, and I need to make sure that all the data is available before continuing.

We specified PartneredLtlData in the transport contents, which got accepted. The transport cost also got estimated.

Should I just stop waiting after a while? I saw the carrier name show up in the Seller Central console on a previous rendition of the same test, quickly after requesting the estimate. Should I call a different operation?

Thank you!