Issue with getting the authorization code using Postman

[thesearchbase]

I am working currently on the Bullhorn integration using the REST API
Right now I am running some tests to get the authorization code using Postman

I have successfully get it to redirect me to the login page of Bullhorn however after I enter my credentials correctly, I receive this message :

Bullhorn OAuth Error
Invalid Redirect URI
Redirect URI: null
Client Id: xxxxxx-xxxxx-xxxxx-xxxxxx
Client Name: xxxxxxxx

Any idea how can I resolve this issue? Do I need you setup something for me first?

Note that the callback url I used is "http://www.bullhorn.com"