Use case generalization versus extension

Question

UML Use Case Diagrams allow for two seemingly equivalent ways to show that a given use case might be realised in several different ways namely use case generalizations as op

Answer 1

An example of an extension would be an "Enter Discount Code" use case. Entering a discount code has to do with making a payment, but you don't have to enter one in order to make the payment.

You can look at the "is a" relationship to make the determination of which to use. Pay by PayPal "is a" make payment, a specific way of making a payment. Enter discount code isn't. It's something additional you can do while making a payment.