Let's say you've got an item that already includes an accessory in it's pricing, but then your client requests an additional instance of that accessory. The example we'll use here is that you have a nacho cheese dispenser that comes with 1 bag of cheese, but you charge for additional bags.
You don't want to enter the additional bags as a separate item in your inventory, since they are all the same. You just want to charge the client if they are getting more than one.
For this type of instance...
First off, you'll want to create the Accessory as an inventory item.
Click Inventory, then click Add Product.
Add in the details for the Accessory inventory item:
Next, let's create a new item to be the main Item (Nacho Cheese Dispenser):
Note: You'll want to mention that a bag is included in the description, since we'll be hiding the first bag from their contract view (see more below):
Make sure you add the Accessory (Bag of Nacho Cheese) to the Relations Tab, and Accessories, then click 'Required', 'Auto-Hide', and how many you'd like to be automatically included in each order.
This will ensure that one of this Accessory (Bag of Cheese) is included when a client orders the Item (Dispenser), and will be hidden from the client view, which means there will be no charge.
Now let's test adding this item to a project!
Select Add Inventory Item and select the Item (Nacho Cheese Dispenser) the Accessory (Bag of Cheese) will automatically add.
Now let's say the client wants an additional bag.
To add (and charge for) another instance of the accessory, simply click the 'Related Item' box next to the Dispenser, and un-check 'Auto-Hide' and add another bag.
Now you can add these items like a pro. After all, it's nacho first time!