Make mandatory coupons for all products in WooCommerce

make-mandatory-coupons-for-all-products-in-woocommerce.php

add_action( 'woocommerce_check_cart_items', 'mandatory_global_coupon_code' );

function mandatory_global_coupon_code() {
    $coupon_code = 'summer2'; // The required coupon code

    // Check if the required coupon is applied
    $coupon_applied = in_array( strtolower( $coupon_code ), WC()->cart->get_applied_coupons() );

    // If the coupon is not applied, prevent checkout
    if ( ! $coupon_applied ) {
        wc_clear_notices(); // Clear all other notices
        wc_add_notice( sprintf( 'A coupon code "%s" is required to complete the purchase.', $coupon_code ), 'error' );
    }
}