By default, WooCommerce displays applied coupon codes in lowercase in the cart and checkout totals. This snippet overrides that label to show the coupon code in uppercase, which looks more professional and consistent with how coupons are typically marketed. Uses mb_strtoupper() for full multibyte and UTF-8 character support, and esc_html__() with the WooCommerce text domain to keep the label translation-ready across all languages.
add_filter( 'woocommerce_cart_totals_coupon_label', 'uppercase_coupon_label_in_cart', 10, 2 );
function uppercase_coupon_label_in_cart( $label, $coupon ) {
return esc_html__( 'Coupon:', 'woocommerce' ) . ' ' . mb_strtoupper( $coupon->get_code() );
}