How can stores under the same organization select different countries in Shopify Payments?

I have two stores under the same organization: a US store and an Australia store. These two stores belong to different legal entities in their respective countries. The US store is the primary store, while the Australia store is newly established.

Here’s the question: when I try to set up Shopify Payments for the Australia store, it only allows me to select the US as the country, not Australia. What adjustments should I make to resolve this? Does anyone know the reason behind this?