Activating a Westfield Digital Gift Card can only occur after you've downloaded the Westfield AU/NZ app and registered for an account.
Once you've completed the registration, return to your email on your phone (this will not work from a PC or tablet), and tap on the activation link to open the Westfield AU/NZ 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).
Once the card has been activated in the Westfield AU/NZ app, tap on the Add to Apple/Google Pay button
Follow the prompts to add the card to the wallet
Once complete tap on Take me to my Digital Wallet to see the card in the Wallet and start spending
If you have an Apple Watch, this device will be made available to you in a connected device list during the Add to Apple Pay flow. You'll need to run-through the above steps again if you want to add to both your iPhone and your Apple Watch.