These steps are not apparent in my QB online screens.  When I click on a customer "invoice", "Receive Payment" is in the upper right hand corner.  I cannot "delete" this. 

I can set the Payment amt to $0; but then at the bottom of the screen  I do not see"Discounts and Credits", I only see Discount-percent, Discount-amt.  I then added a Description "Bad Debt" to clarify and Save.

 I see the invoice is now $0. I am unclear if this is processed correctly.