The background vocals are loud though? Did you watch the same video as me? As soon as the chorus starts, the backgrounds are WAY louder than her voice (and even consume her voice at various points). Her voice is naturally pretty light and delicate like Selena Gomez too (who also gets called out for lip syncing despite there being 100s of videos and live accounts proving she can sing). Also when using that mic-piece, it doesn't pick up your voice as well as a microphone would which is another factor in her lower than usual vocals (you can even google that if you want receipts).

If you don't like Zendaya or her song, then that's fine. Don't just sit there and lie about her lip syncing just so you can feel better about yourself.

Oh and I bolded the clear reaching because you just don't like Zendaya so it's easier to come to that conclusion than actually admitting she did okay on her first televised live performance. I'm done responding to you, now. Have a nice day.