Here is a quick solution to resolve the issue of not being able to add the card to Apple Pay. Please note that this cannot be solved by changing your Apple ID country/region.

Anyway, in order to add your card to Apple Pay, all you have to do is go to your General settings, then navigate to Language and Region. On the Region settings, change the country (the country where your bank is). Please note that my experience is with Suncorp Bank, so your settings might vary.

With this simple adjustment, you can now easily add your card to your iPhone.

I hope this quick guide proves helpful in resolving any similar issues you may encounter. Thank you!