How to change currency?

I am in New Zealand and have an older NAS I want to purchase a support contract for.

I go through the New Zealand website but when I go to purchase it shows the currency in AUD.

That's normally fine as the currency usually converts automatically (and if I use the paypal page it shows the currency in both NZD and AUD with the conversion rate)

but a banner then shows on top of the page "new plan does not have a rate schedule with a currency matching the account's currency"

If I try to proceed using credit card or paypal it then has a banner saying "Oops! Something went wrong."

is there a solution available for this?