unable to chose default country and state

trying to limit to Australia > NSW. I have tried a few things including the below.

// default checkout country
add_filter( 'default_checkout_billing_country', 'change_default_checkout_country' );
add_filter( 'default_checkout_shipping_country', 'change_default_checkout_country' );
function change_default_checkout_country() {
    return 'PK'; // country code
}

// default checkout state
add_filter( 'default_checkout_billing_state', 'change_default_checkout_state' );
add_filter( 'default_checkout_shipping_state', 'change_default_checkout_state' );
function change_default_checkout_state() {
    return 'SD'; // state code
}

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