Inventory - Basic Question - Reduce quantity trigger

Inventory - Basic Question - Reduce quantity trigger

Hi,

I am just adding inventory for the first time to our system.  Can you confirm when the inventory quantity is deducted?  Is the quantity adjusted when you SEND the invoice to the customer or when the customer actually PAYS for the invoice?

I ask because I have open invoices (sent but not paid) and I am not sure if the items in the open invoices should still be counted in the inventory total.

If the inventory trigger is PAYMENT, how does zoho deal with inventory for partial payment? I sent an invoice to a customer and they paid for 50% as a deposit.  The balance is still due.  Are all the items deducted from inventory?

Thank you,
Allison