To use methods such as Afterpay, Laybuy, Zip or Klarna, these payment methods would need to be shown on the item's listing, located underneath the item's price, as shown below.
Some of these methods have a minimum and/or maximum order limit too. For example with AfterPay, if the total of your order is over $2000.00, AfterPay cannot be used to pay for the order.
Zip is not eligible for pre-order items, so if an item is on pre-order, Zip will not be available at checkout.
You would also need to use a verified address in order to use these payment methods, and you can read more about setting that up here.