Attributes in WooCommerce needs be added in two files, as they are used to sync products manually and automatically when changes are made in the webshop.

These are the files:
in the function add_product 

in the function product_endpoint_callback in $productArray

Each attribute is structured like this:
'sku'   => $product->get_sku(), 

where 'sku' defines the name you want it to have in, and => $product->get_sku(), is a WooCommerce logic for pulling the attribute.

Finally, go to -> Data and click Start New Data Sync to import your new attributes.

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