To retrieve the Client Id and Client Secret Key:

• Login to your Allegro seller panel.
  
• Register for the new Allegro Application by entering the Application Name, Application Description, choosing the type of application.
• Paste the Redirect Url here which you had copied earlier into the Url to redirect section.
• Then by accepting the rules click on ADD.
• After adding the navigation window appears as shown below where you get your Application Name, Type, Client Id, and Secret Key:
  
• Now you can copy the client Id and Secret key from here and paste it in the API settings.