Are retro billing and Self-billing referring to the same process?
 
Answer:
 
Retro billing and Self-billing are entirely different processes and can be executed independently.
 
Let me explain using a very simple example:
 
You sell 10 units of a material A for $100 per unit - Amount $1000
 
Invoice is sent to customer for $1000 on say Sep 20, 2099
 
RETRO-BILLING
 
Now due to price negotiations price may change to $90 w.e.f Sep 01, 2099. Thus you will update your price conditions in VK12 for this material/customer to $90 with validity from Sep 01, 2099. But as you have already invoiced the customer in past so to take care of the extra billing . You will execute retro-billing process.
 
You will go to VFRB and enter the selection criteria for the material and suitable dates, system will provide you the list of candidate invoices to which this price reduction is applicable and hence you can simulate or even execute retro-billing after providing Cr/Dr memo type and order reason. These documents will get attached to the original invoice 
 
Important to Note - you must maintain the 'use of order reason for retro-billing' in Order reasons configuration for this to work properly.
 
SELF-BILLING
 
Here customer raises invoices for itself. Supplier does not send the invoice to customer. 
 
Customer may send a self-bill for the above case like $80 a piece. This will hit the supplier system in form of EDI/Fax/Paper etc and on verification in system will show in Self-bill Monitor VSB1n.
 
On processing, system will generate a credit memo of $200 for the customer and a debit memo for same amount with reference ?_?_?. 
 
Now the customer while paying will pay $800 as per its self-bill and the same would be settled against original invoice of $1000 and SB credit Memo of $200. Other debit memo of $200 (with ?_?_? reference) will remain open in system which may be cleared off by a retro billing run where supplier may reduce the price by $20 or take further action as needed.

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