Variable Product Meta – Custom Field 2

I’ve been working with this code: https://docs.woocommerce.com/document/shipstation-for-woocommerce/#section5

but I am having no success. I believe this could be due to this being a variable product? Can the plugin pass custom field data from a variable product into the custom field 2 section in Shipstation?

Here is the code I currently have in functions.php

}
// Add this code to your theme functions.php file or a custom plugin
add_filter( 'woocommerce_shipstation_export_custom_field_2', 'shipstation_custom_field_2' );
function shipstation_custom_field_2() {
    return 'iconic_cffv_5723_style'; // Replace this with the key of your custom field
}

any guidance is appreciated.

Graham

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