add_action('wp_ajax_add_transfer', 'process_add_transfer');
add_action('wp_ajax_nopriv_add_transfer', 'process_add_transfer');
function process_add_transfer() {
     global $woocommerce;
     wc_add_notice( 'This is my custom error', 'error' );
     wp_redirect( get_permalink(125) ); //this is the same page form is on
}

wc_print_notices();

do_action( 'woocommerce_set_cart_cookies',  true );