Login with Okta on thick powerbuilder application

I need to implement the login with Okta on a thick client coded with Powerbuilder (non-web language).
I have coded the Resource Owner Flow, and it works. I can get an access token.
But as I can read that Resource Owner Flow is not recommended, and maybe forbidden by Oauth2, I try to continue with Authorization Code Flow.
I have a problem with the login redirect URIs that doesn’t exist for me and I don’t know how to handle it.
Any advice?
Thanks in advance.