How to display a Rails flash notice upon redirect?

redirect_to new_user_session_path, alert: "Invalid email or password"

in place of :alert you can use :notice

to display

Remove the .now. So just write:

flash[:notice] = 'Successfully checked in'
redirect_to check_in_path

The .now is specifically supposed to be used when you are just rendering and not redirecting. When redirecting, the .now is not to be used.