Unable to login via rest API

I am using the community version to develop a proof on concept. I am trying to create the ability for users to create their own account via a web application. To do this I am planning to create a standalone web service with administrator credentials to create the accounts.

The problem that I am having is that when I try to login to the portal via the API it returns

“Unable to log in. Please check your username and password”

With Interceptor installed I can login via the portal and successfully execute other API calls via Postman.

I have resolved this issue by selecting the x-www-firm-urlencoded option for Body in Postman.