Create Virtual Coupon in Woocommerce to have custom discount on the cart

addVirtualCoupon.php

// add the below code to your theme's functions.php 

/*'woocommerce_get_shop_coupon_data' is used to add virtual coupon*/
add_filter('woocommerce_get_shop_coupon_data', 'addVirtualCouponDiscount', 10, 2);
add_action('woocommerce_cart_calculate_fees', 'addCoupontoCart');


function addVirtualCouponDiscount($data, $coupon_code) {
  if($coupon_code == "virtual_coupon") {
      $coupon = array(
                "discount_type"=>"percent",
                "amount"=>"30",
                "individual_use" => false
      );   
      return $coupon;
  }
}
function addCoupontoCart() {
  $coupon_code = apply_filters('woocommerce_coupon_code', "virtual_coupon");
  //code to create virtual coupon
  $coupon = new WC_Coupon($coupon_code); 
  if(!WC()->cart->has_discount($coupon_code)) {
    WC()->cart->add_discount($coupon_code);
  }
}