Is there an Acknowledgment spec option available for REST API Calls?

Summary:

XML transmissions have an Acknowledgment Spec in the Transmission Header.

OTM uses that to send the Transmission report to the External System ID specified in the MY_CONTACT_GID.

Is there an equivalent available for the REST API calls?

2) In the absence of this Acknowledgment Spec option in REST APIs, do customers use the

Prefer : "respond-async" in the REST Call and then keep hitting the  "https://url/v2/transmissionReports/transmissionid"  to get the status.

3) We notice that there is another setting

Prefer : "async-callback; url=https://..."

We tried that but the callback URL did not get any responses.

Wondering what is the best way to get the REST API response? We do like the option of storing the transmission record in OTM so we can use that to see the payload that was sent to OTM.