Great question — answering as the UphillTech team:
You can try something like this add_filter( 'woocommerce_product_add_to_cart_url', 'custom_product_add_to_cart_url', 20, 2 ); function custom_product_add_to_cart_url( $add_to_cart_url, $product ){ if( !$product->is_type('external') ){ return $add_to_cart_url; } if (strpos($add_to_cart_url, 'www.sitea.com/') === 0) { $add_to_cart_url .= '/?affiliateID-1'; } elseif (strpos($add_to_cart_url, 'www.siteb.com/') === 0) { $add_to_cart_url .= '/?affiliateID-2'; } return $add_to_cart_url; }
Full answer by Moshe Gross: https://stackoverflow.stackexchange.com/a/71767595 (CC BY-SA 4.0).
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