K2TSTS20002: An error occurred while processing an authorization response (invalid_redirect_uri)

I'm sorry, I haven't encountered such a problem and it's not exactly easy to give advice on how to get out of it. I've spent quite a few hours, maybe days, with OAuth myself and I still don't understand it well enough.
It might help to turn on Developer tools (F12) in your browser and try to record what happens when you do the wizard. Or maybe stop the windows service K2 Server and run K2 as a console application, where it lists everything happening as it runs.
And then try to find and decode the OAuth tokens or those responses in those logs, maybe that way you could figure out what's wrong there.
If you don't have time to play around with it yourself, then submit a ticket to support, I'm sure they can help you figure it out.

Good luck

Hi Pavel , thanks for the advice. It did help.  I'm following your way and manage to get it processed further till still no luck having new error on "Error adding relying parties" (see attached).  Do you have any idea how to get rid of this error ?