When you make your reservation, make sure you go to www.united.com and click on the link next to Fare finder that says "More options" near the top left corner. This will prompt you for the login screen. I used to go to "Planning travel" near the bottom left and click on "Shop for flights". But some time in the middle of this year, this link no longer takes me to the login screen. So I rang united.com support, and they told me about the proper place to click on.