Restrict Coupon Code for a user. if the user is who you want, the coupon code will add to the cart.

single-user-coupon-code.php

add_action( 'woocommerce_applied_coupon', 'check_for_individual_discount' );

function check_for_individual_discount()
{
	global $woocommerce;

  // Get All Coupons in Cart
	$cart_coupons = $woocommerce->cart->applied_coupons;
	$last_element = count($cart_coupons) -1;
	$last_added_coupon = $cart_coupons[ $last_element ]; //get the last added coupon to the cart
	
	$coupon_array = array();
	$coupon_array = explode('-', $last_added_coupon);
	
	if( count($coupon_array) == 3 && $coupon_array[0] == 'fgccu') //if this coupon is for one user!
	{
		//get user id
		$userid = $coupon_array[2];
		
		$current_user = wp_get_current_user();
		if($current_user->ID != $userid) // if coupon user id is not equal with current user id remove the coupon!
		{
			wc_clear_notices();
			wc_add_notice('This Code Can not use for Current User! 'error');
			$woocommerce->cart->remove_coupon( $last_added_coupon );
		}
	}
}