In SAP, the transaction codes VKOA and OB40 serve different purposes and are used in different contexts within the financial and controlling modules. Here’s a breakdown of the differences between the two:

VKOA (Assign G/L Accounts): VKOA is a transaction code used in the Sales and Distribution (SD) module. It is used to assign general ledger (G/L) accounts to various account determination keys in SD. The account determination keys are used to determine the appropriate G/L accounts for different types of transactions, such as revenue, discounts, taxes, etc. VKOA allows you to specify the G/L accounts that should be used for each account determination key, ensuring accurate financial postings in SD.

OB40 (C FI Maintain Table T030): OB40 is a transaction code used in the Financial Accounting (FI) module. It is used to maintain the account determination for automatic postings in FI. OB40 provides a central configuration area where you can define which G/L accounts should be automatically posted for specific transaction types, such as vendor invoices, customer payments, asset postings, etc. By maintaining the account determination in OB40, you ensure that the correct G/L accounts are automatically determined and posted during FI document processing.

In summary, the main difference between VKOA and OB40 is their usage and the modules they are associated with. VKOA is specific to the SD module and is used to assign G/L accounts to account determination keys for accurate financial postings in SD. OB40, on the other hand, is used in the FI module and allows you to maintain the account determination for automatic postings in FI, ensuring the correct G/L accounts are used during FI document processing.

For example if condition class is D then system considers it as TAX and the account key controlled by FI assignment in OB40 but if the condition class is A then it is more about Revenue/Surcharge so only VKOA is maintained.