In SAP billing process; I am facing the problem with the exchange rate. As the rates picked in the sales order as default exchange rates maintained for the day; if the sales order is MTO and goods will dispatched after 2 months and within these 2 month the exchange rate got floated by a large amount and during the billing with VF01 t-code; the exchange rate will be something else; and I can’t change it at that instance also. 

The billing document will be posted to the accounting after getting the money from the customer and the exchange rate will become something else at this moment also; and make a large difference of amount at this instance. Is there is any provision in sap system so that I can change the exchange rate in the billing document and with this same exchange rate I can post the entries in accounting also. It will solve the problem as it will give me the billing amount in exact LC amount also.

Solution: 

You can have the same exchange rate (OB08) in sales order to be in billing document:

In Copy control VTFL at item category level -> PricingExchRate type to 'A'Copy from sales order

Now, if you want that same exchange rate to be in Accounting document in Sales Order GOTO -> HEADER -> ACCOUNTING there one field is there 'Exch.rate-acct.' enter the exchange rate there manually, which will post to accounting.

In the billing document there are 3 exchange rates, please review:

VBRP-KURSK 
Exchange Rate for the conversion Loc.currency <-> Doc.currency.
for Price Determination
The determination of this exchange rate depends on the setting
of TVCPFLP-PFKUR in customizing copy-control

VBRK-KURRF
Exchange Rate for the conversion Loc.currency <-> Doc.currency.
For FI postings
If there is a manual entry in the sales order field VBKD-KURRF (Goto -> Header -> Accounting), then it is copied into VBRK-KURRF.
Otherwise VBRK-KURRF is determined during invoice creation.
It is supposed that manual entry has higher priority.
See the OSS note 36070.

KOMV-KKURS 
Exchange Rate for the conversion Cond.currency <-> Loc.currency
At price condition level.
It is always determined according to the Pricing date.
See the OSS notes 92613, 97487.

During VF01 the system determines the Exchange rate for FI posting
VBRK-KURRF from the currency tables according(OB08) to the billing date only if the field Exchange rate for FI posting is empty in the source sales document (VBKD-KURRF).
If the sales document has this field filled, manually or copied from a reference invoice (by copy control routine), then it is copied in the subsequent billing document. This is the standard working of the system.

The exchange rate should be based on your configuration in copy control (VTFA or VTFL) at the item category level. The choices you have are as follows:

Pricing Exchange Rate Type (V_TVCPFLP-PFKUR)
A Copy from sales order
B Price exchange rate = Accounting rate
C Exchange rate determination according to billing date
D Exchange rate determination according to pricing date
E Exchange rate determination according to current date
F Exch.rate determination accord.to date of services rendered

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