Macbook Pro 2023 - Facetime can make calls, but cannot receive them.

I'm trying to help my mother with her Macbook Pro. She does not have an iPhone. She used to be able to receive calls on FaceTime, but ever since she got the new Macbook, she cannot. She can call me, but if I call her, it simply shows as a missed call immediately. It doesn't even give an option to answer the incoming call. I've used remote access to test this. There is literally nothing on Google that shows how to solve this problem. It is not a network issue because she can call me without issue.

My dad also tried calling her FT from his iPhone, same issue.

Under FT Settings, she's logged into her Apple id, and You can be reached for FT at: is checked although greyed out.

Any ideas?