Tumblr new post APIs not working

Have been trying to get the Tumblr new post APIs working for quite some time. Unfortunately, I am getting errors each time I try these.

Been following the api docs judiciously - to no avail.

All other data fetching works find, even with OAuth.

I am using Postman for the requests.

A working curl request that creates a new post on a Tumblr blog from the bash/terminal will be of great help.

Thanks,
Sarthak