In the context of OAuth and Saxo Bank the redirect field provides a URL whereto Saxo Banks authorization server will redirect after a user has successfully authorized your application. Therefore this value depends entirely on what you are trying to achieve.
If you are still developing your application you might want to redirect to localhost on your machine or if you are live this may be a different URL. In any case the redirect URL page is where the user should go after logging in with their credentials.
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