Force COD orders to 'on hold'

wc-hold-cod-orders.php

<?php // only copy if needed

/**
 * Forces orders be marked as "on hold
 */
function sv_wc_cod_order_status( $status ) {
	return 'on-hold';
}
add_filter( 'woocommerce_cod_process_payment_order_status', 'sv_wc_cod_order_status', 15 );