Without sharing too many spoilers... I solved the challenge but the check script was unhappy. The curl commands in the script worked fine, the earlier parts of the script failed, i.e. it didn't like how I'd decided to make that work.

This kind of thing annoys me. This is why CTFs are great, where the goal is to get the flag string. Obviously harder to do for sysadmin, but expecting a particular configuration when I managed to make it work without doing things exactly as they wanted is no better than a poorly written exam.