With Alamo rentals through Costco, you do not enter your Alamo Insider number on the Costco site. Rather, the Costco confirmation includes an Alamo confirmation number as well as the Costco confirmation number. Then, login to the Alamo site and link the reservation to your Alamo Insider account using the supplied Alamo confirmation number. This has worked for me every time, 4 or 5 rentals per year, for a number of years. I’ve already linked my January reservation.Did you plug in your Alamo member ID on the Costco website? I just did a Avis rental through Costco and was able to skip counter. I know on one rental through Costco they won't let you plug in your member number so I don't use that one.