In the next step Create Connected App you need the DocuFlow OAuth Callback Url. This page describes how to open the DocuFlow Settings page where you can get it.
Instructions
Search for DocuFlow Settings in the App Launcher:
Press Settings:
The DocuFlow login page will start in a new browser tab. Fill in your Username (Gebruikersnaam) and Password (Wachtwoord) and press Inloggen:
Choose Salesforce > Settings in the menu on the left side and keep the page open while you continue with the next step: Create Connected App