Whether I need to repay 60 days of fasting or not

Asalaam alaykum, I broke my fast today because I hadn’t eaten properly my Iftar yesterday and slept until past fajr today.

I was meant to take a short nap and wake up and eat. I had my food prepared and I either set an alarm which I didn’t hear or slept before I could set it (I don’t remember because I obviously didn’t wake up)

I told my mum and she said it’s not a valid reason I need to fast for 60 days. I’m not sure if that still applies since I had the intention to fast and I hadn’t known about the 60 days kaffarah thing until after I broke my fast.

Please give me some insight