function merge_additional_checkout_data( $customer_data, $order ) {

    if( isset( $customer_data['Test: Drip Subscription via WPFusion 1'] ) ) {
        $customer_data['wpfusion'] = $customer_data['Test: Drip Subscription via WPFusion 1'];
    } else {
        $customer_data['wpfusion'] = null;
    }

    return $customer_data;

}

add_filter( 'wpf_woocommerce_customer_data', 'merge_additional_checkout_data', 10, 2 );