I recommend to googling first before made a thread, many way and steps to get method to use gift cards.
It's not that easy. ebay has limits and requires you to link a PayPal account. Sometimes or actually most of the time the PayPal linking will get an error because they detect something suspicious
A large possibilities of chance for that your PayPal account will get a limit and review by PayPal because they're will feel suspicious about your account and then if get a limit the problem will become a more complicated.