iPhone 15 and MAC "aren't on same Wi-Fi network" but they are

I've been trying to make phone calls through Facetime with the iPhone 15 and Sequoia 15.2 on an M1 Mac, but every time I try, I get the message, "iPhone not available. Your iPhone and Mac must be on the same Wi-Fi network." However, when I try to start a call on my iPad (on the same network), I have no problem with my iPhone.

It used to work fine until I switched phones (from SE 2020 to iPhone 15), and no matter how often I restart the phone and computer, turn off/on Wi-Fi, or switch off/on the Phone options, I get the same message.

I don't know where else to look to fix this.