Hi AmitGohel,
are you already using V12.2? Because this REST-endpoint was introduced in V12.2.
Make sure that the data are in the body of your request and format is set to application/json.
You should also use a "full qualified" user-name <client>/<id>/<department> e.g. 100/AG-1/CDA-USERS
{
"name": "100/USER-20190304/AUTOMIC",
"password" : "1234",
"display_name": "Test User",
"is_active": true,
"type": "User",
"description": "user is created by REST",
"email_address": "test@email.com",
"phone_number": "1-555-1234 5678",
"is_admin": false,
"authentication_method": "UC4"
}