Activating a Westfield Digital Gift Card can only occur after you've downloaded the Westfield Plus app and registered for an account.
Once you've completed the registration, return to your email and tap on the activation link to open the Westfield Plus app. Once you "Add Gift Card to account", the card has been activated.
Once a card is activated, the link from the email cannot be used again or transferred to another person.
In order to start using the card, you need to add the card to your Apple Wallet or Google Pay wallet.