As advised, do not deal with this 'buyer'. It is a scam.
The buyer will bid on and win an item. They will ask you to add a gift voucher and offer you money over and above the value of the voucher.
They will ask you for you phone/email details.
You will get a message via WhatsApp or an email confirming that the buyer has paid and urging you to get the item sent.
This a scam. (Yes, I know I have said this already.)
This is not a genuine sale.
Not a genuine buyer.
No payment will have been made.
Never agree to add a gift voucher.
Only ever send items that are in 'sold' items when you are logged onto Ebay and show as 'paid - post now'.
Buyers do not need your email address or phone number and Ebay never tell you that payment has been made via WhatsApp.
"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)