Shopify dont allow me to make my purchase when i login for NZ

Hi Ring Support,

It appears you guys have issues on your login page for users in NZ making a purchase on the AU website.

Upon adding items to cart it works as a guest visitor on your AU site, but as soon as i login it takes me to a Shopify error page. This have been occurring for very long now.

Now i cant make a purchase unless you send me an email reminder to complete my abandoned cart as a guest user which means i cant get my subscriber 10% discount. Help please!