I Phone 7 and Facetime

I set-up an old I Phone 7 that I had for my grandson and it is not allowing us to FaceTime. Is that something that I Phone 7 can not do? It has the most current update that is allowed for the version of the phone (IOS 15). He is connected to Wi-Fi but not able to even call using Wi-Fi. Can any one share if there is a fix for that issue or if it is not supported on the 7. Thank you.