I think I’ve found the root cause of this. I had updated a library version in my build.gradle, but I had not updated the pre section of my circle.yml file to fetch the corresponding files. Hence, this message was really saying: “You don’t have these libs”, rather than “you haven’t agreed to the license”.
Note, this is a great summary of how to download the needed files while also caching them: Android SDK Support Library 24 - #5 by drazisil