Hi,
Code shared on this video around 16min or so has some mistakes on the for loops. I’m sharing mine below.
AddToFirstEmptySlot method has 2 params. Second param is item count.
For loops in the original code has index starting from 0, so the item count also ends up 0. I just changed the loops to start from 1 to reward.number inclusive. All credit goes to the fellow classmate who shared method in the video.
Hope this helps some head scratching 
Thanks so much for the great course.
private void GiveReward(Quest quest)
{
foreach (var reward in quest.Rewards)
{
if (reward.item.IsStackable())
{
var added = GetComponent<Inventory>().AddToFirstEmptySlot(reward.item, reward.number);
if (!added) GetComponent<ItemDropper>().DropItem(reward.item, reward.number);
}
else // if not stackable give or drop several units
{
var given = 0;
// add all possible to empty slots
for (var i = 1; i <= reward.number; i++)
{
var added = GetComponent<Inventory>().AddToFirstEmptySlot(reward.item, i);
if (!added) break;
given++;
}
// if entire reward is given go to next reward.
if (given == reward.number) continue;
// if given less then in reward, drop the difference
for (var i = 1; i <= reward.number; i++)
{
GetComponent<ItemDropper>().DropItem(reward.item, i);
}
}
}
}