Custom nested attributes

I am generating a product feed for Marktplaats (Example feed) in the product feed pro plugin for WooCommerce.

Product feed pro has a preset Marktplaats feed, but it misses some necessary attributes. This would normally not be an issue because you can easily add product attributes, however I need to add nested attributes.

Here is an example of one of the nested attributes I need to add:

<admarkt:shippingOptions>
            <admarkt:shippingOption>
                <admarkt:shippingType>PICKUP</admarkt:shippingType>
                <admarkt:location>1097DN</admarkt:location>
            </admarkt:shippingOption>
            <admarkt:shippingOption>
                <admarkt:shippingType>SHIP</admarkt:shippingType>
                <admarkt:cost>695</admarkt:cost>
                <admarkt:time>2d-5d</admarkt:time>
            </admarkt:shippingOption>
        </admarkt:shippingOptions>

I have added the custom attributes to the products with?the advanced custom fields plugin. I have mapped the attribute field groups. Field groups are generated and work fine. The parent and child attributes show up in the Product Feed pro plugin. When I choose the parent attribute “shippingOption”, it just comes out blank.

The plugin has built in nested groups the look like this:

Plugin:

plugin shows the child fields entered, no parents need to be selected

The XML then looks like this (which is correct):

<admarkt:budget>
<admarkt:totalBudget>20</admarkt:totalBudget>
<admarkt:dailyBudget>5</admarkt:dailyBudget>
<admarkt:cpc>0.09</admarkt:cpc>
</admarkt:budget>

How can I make a nested group in my feed like show above, but custom? That’s all I need!