The problem is that you send only 1 menu
you need to send 2 like
AddGossipItemFor(player, GOSSIP_ICON_MONEY_BAG, "|TInterface/ICONS/Ability_Spy:30:30:-18:0|tBack..", 3, 0);
AddGossipItemFor(player,GOSSIP_ICON_MONEY_BAG,"<==Back", 4,0);
SendGossipMenuFor(player, 800002, creature->GetGUID());
I hope you understand what I m saying