Bullhorn OAuth Error - Invalid Redirect URI

[works21]

Hi,
i am also new to Bullhorn, i used Postman to authenticate but i get the error.

Bullhorn OAuth Error
Invalid Redirect URI
Redirect URI: null
Client Id: 7438d6ed-58b0-4f25-8ecf-17e9223b8bec
Client Name: Balkenende Personal Intelligence - 21199

On the board i saw many people with the same problem.
I tried the callback-url without and with https://www.bullhorn.com (or http://) , no succes.
i used:
https://auth-emea.bullhornstaffing.com/oauth/authorize
https://auth-emea.bullhornstaffing.com/token
client ID and secret password

ref:_00DU0YOky._5003g9D7Zh:ref

Can you put me in the right direction.

Thanks in advance Bram