Your bracelet is in the right category and, as a Cartier gold bracelet with a start price of over £500, Ebay should definitely have added the authenticity guarantee.
I would contact Ebay Customer Services to see if there is a glitch and ask them to add it. The authenticity guarantee protects you as well as the buyer.
Use the link below to get a callback.
They will need the item number so have that ready.
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)