C++ "invalid key to 'next'" when trying to read a list inside a LUA STATE in C++

[Shaykie2]

I'm trying to add elements to the NPC Trade, so when the "luaOpenShopWindow" method is triggered I'm sending a list of IDs and Quantities, something like this:

{"id":2160,"buy":5000,"sell":0,"requiredItems":[{"count":10,"id":2152}],"subType":1,"name":"crystal coin"}
{"id":2520,"buy":1,"sell":0,"requiredItems":[{"count":1,"id":7618}],"subType":1,"name":"demon shield"}

This is my adapted code:

        lua_getfield(L, tableIndex, "requiredItems");
        if (lua_istable(L, -1)) {
            std::list<ShopRequiredItem> requiredItemsList;
            lua_pushnil(L);
            while (lua_next(L, -2) != 0) {
                const auto tableIndexReqItem = lua_gettop(L);
                if (lua_istable(L, tableIndexReqItem)) {
                    ShopRequiredItem reqItem;

                    reqItem.itemId = tfs::lua::getField<uint32_t>(L, tableIndexReqItem, "id");
                    reqItem.count = tfs::lua::getField<int32_t>(L, tableIndexReqItem, "count");

                    requiredItemsList.push_back(reqItem);
                }

                lua_pop(L, 1);
            }

            item.requiredItems = requiredItemsList;
        }

For the first item it gets the values normally and populates the variable correctly.

Now in the second item that it goes through, whether or not there is a second item in this "requiredItems" it gives the error "invalid key to 'next'"

Can anyone help me?