Not working zv_is_player_vip(index)

[YankoNL]

I made a plugin for VIP's Online and I noticed that this function isn't working. I didn't find a way to fix the function, so instead I need to use this method for checking if the player is VIP in every plugin.

stock is_vip(id)
{
	if(!cvar_exists("zp_vip_flag_acess")) return 0;
	new g_szFlags[32];
	get_cvar_string("zp_vip_flag_acess", g_szFlags, sizeof g_szFlags -1);

	return get_user_flags(id) & read_flags(g_szFlags)
}

Can you fix it?