I ended up making less than I estimated when signing up for health insurance but now it's saying that I owe some aptc back, how is this possible?

I had to go on a medical leave absence in 2022 for almost 6 months, I was only paid 60% of my pay. But now in putting my numbers on my return, I'm being told that I owe some of the aptc back I don't understand why that would be since I overestimated my income