Screen Based API json?
Have you seen this Help article?
Also, you can import a starter kit into Postman:
1. Go to the Web Service Endpoints (SM207060) screen and click VIEW ENDPOINT SERVICE -> OpenAPI 2.0
2. Save the raw data to your Desktop. I think it depends on your browser, but this is what it looks like for me in Firefox (I saved the file to my Desktop as swagger.json):
3. Open Postman and do File -> Import... and choose the file that you just created on your Desktop
4. This will create a Collection with 740 request examples that you can browse through: