To send or retrieve/ get binary data from an API, you can add the below Content-Type as a header in the HTTP Service step.
application/octet-stream
The header in your HTTP Service step will look like the below image.
Find out more about the "Content-Type" header by clicking on the below link:
For more information on MIME types, please click on the below link:
For the available MIME types that can be used , please click on the link below: