Snippet to apply coupon to WooCommerce cart

apply-coupon.php

<?php

add_action( 'woocommerce_before_cart', 'apply_matched_coupons' );
function apply_matched_coupons() {
    $coupon_code = 'renewal20'; // Replace with your own coupon code
    if ( WC()->cart->has_discount( $coupon_code ) ) return;
    
	// APPLY COUPON WITHOUT ANY CONDITIONS
    WC()->cart->apply_coupon( $coupon_code );
	wc_print_notices();

	// APPLY COUPON IF PRODUCT ID IS IN CART
	foreach ( WC()->cart->get_cart() as $cart_item_key => $cart_item ) {
		$discountedProducts = array( 186, 187, 188 ); // Replace with your own product ids

		if ( in_array( $cart_item['product_id'], $discountedProducts ) ) {   
			WC()->cart->apply_coupon( $coupon_code );
			wc_print_notices();
		}
    }
	
	// APPLY COUPON IF CART TOTAL IS MORE THAN 30
	if ( WC()->cart->subtotal > 30 ) ) { // Replace with your own total   
		WC()->cart->apply_coupon( $coupon_code );
		wc_print_notices();
	}
}

?>