...
<item name="foo_payment" xsi:type="array">
    <item name="isBillingAddressRequired" xsi:type="boolean">true</item>
</item>
...

<item name="foo_payment" xsi:type="array">
    <item name="isBillingAddressRequired" xsi:type="boolean">true</item>
    <item name="children" xsi:type="array">
        <item name="issuer_id" xsi:type="array">
            <item name="component" xsi:type="string">Magento_Ui/js/form/element/select</item>
            <item name="displayArea" xsi:type="string">foo</item>
            <item name="template" xsi:type="string">ui/form/field</item>
        </item>
    </item>
</item>

<!-- ko foreach: getRegion('foo') -->
<!-- ko template: getTemplate() --><!-- /ko -->
<!-- /ko -->

<!-- ko foreach: $parent.getRegion('foo') -->
<!-- ko template: getTemplate() --><!-- /ko -->
<!-- /ko -->

<item name="payments-list" xsi:type="array">
    <item name="children" xsi:type="array">
        <item name="foo_payment" xsi:type="array">
            <item name="children" xsi:type="array">
                <item name="issuer_id" xsi:type="array">
                    <item name="component" xsi:type="string">Magento_Ui/js/form/element/select</item>
                    <item name="displayArea" xsi:type="string">foo</item>
                    <item name="template" xsi:type="string">ui/form/field</item>
                </item>
            </item>
        </item>
    </item>
</item>