The request body is in x-www-form-urlencoded format.

An example body for authorization_code flow would look like:
code=yourauthcode&client_id=client-id&client_secret=alhjad^7hhg&grant_type=authorization_code&redirect_uri=https%3A%2F%2Fwww.hcss.com

An example body for client_credential flow would look like:
client_id=client-id&client_secret=alhjad^7hhg&grant_type=client_credentials≻ope=heavyjob%3Aread%20dis%3Aread