Hello @Alex12998
Many, many hosts are receiving this type of fraudulent request and personally I would flag this person to stop other hosts receiving this type of request. They want to get you to go off platform which is against Airbnb's T&C and they should be reported.
In the message part, you'll see three little dots where in their message, click on this and you can report this guest.
When you say that you "approved" this guest, was this a pre-approval by any chance or did you accept their request to book? Two different things. Either way, you can contact customer support and they should cancel this reservation with NO PENALTY for you as they are not adhering to their terms.
Let us know how you get on and come back if you need clarification
Joëlle