Getting problm in unl diagrams

plzzz help me out in this
i m finding a problm in making sequence diagram
problms r
1: response of system should be to UI back or not who initialize a sequence
as in ma system’s working after login controls moves on next interface after validation from server

I’m sorry that I don’t quite get your question. Would you mind explain in more details on what you want to do?

Best regards,
Rain