How to check a car seat

I went to check a car seat as baggage in Detroit. As I made my way through the kiosk prompts, it instructed me to select “yes” under special items and then directed me to see a check in agent. When I get to the agent, she says that I should have checked no. It seemed that at least the agent next to mine confirmed this was the case.

When I checked the car seats in Boston, I clicked yes under special items at the kiosk and had no problems.

Now I’m confused and frustrated because it means different queues (and hence different times) so I would have planned differently.

Does anyone have any insight?