Rest API

I am trying use the Login to Acumatica Rest API with Postman. 

​​According to the documentation I have found in the web, I should be using http://MyCompany.acumatica.com/entity/auth/login as URL

The body as detailed below:

{
"name":"johnd",
"password":"johndpassword",
"tenant":"mytenant"
}

I get an error in Postman as detailed below:

{"message":"An error has occurred.","exceptionMessage":"Error: Invalid credentials. Please try again.","exceptionType":"PX.Data.PXException","stackTrace":" at PX.Data.PXLogin.LoginUserImpl(HttpContext httpContext, String userName, String password)\r\n

What am I doing wrong?