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Many companies have multiple systems interfaces with SAP. Some companies use to post AR and AP transactions into the SAP system from a non SAP system. This blog post will help you to design the FI AR-AP interface to post documents from Non-SAP systems. You will learn the key points that need to be taken care of while designing the interface program to post documents in SAP from non-SAP systems.

Field Selection:

Every interface requires field mapping with a non-SAP system (Legacy system) to post the document in SAP. Some fields are mandatory to post the AR and AP documents, like Posting date and Document date, Document type, Amount, GL account, Customer or Vendor, etc. Besides, you need to identify the fields that are required by the business for their processes, like reference, assignment, and text, etc. Accordingly, map all the SAP fields with a non-SAP system. Consider and provide the proper field details to the legacy system like Field length, Decimal places, the data type of field (date, Char, Numbers, etc.

Exchange Rate:

The exchange rate is very important when we develop an interface in SAP to post the documents.  The amount in local currency should always match in both the systems to avoid any discrepancies and to keep your financial statements intact in both systems.

  • Generally, all systems allow users to enter the exchange rate manually at the time of posting documents, hence always prefer to get the exchange rate from the non- SAP system, which is the actual exchange rate in the document.

  • If you do not want to use the exchange rate from the non-SAP system then, you can get the amount in transaction currency and local currency from the non-SAP system, so there will be no possibility of discrepancies in both systems and the data will be in sync.

  • If there is a single decimal place difference also, it can lead to a discrepancy in local currency amounts in both systems. Ensure that the decimal places in the exchange rate are the same as SAP and your legacy system.


While posting documents for AR and AP always prefer not to calculate tax amounts in SAP. If there is a manual change in tax amounts in the legacy system then the tax amount can differ in both the systems. Tax amount differences can also arise due to rounding rules in both systems. This will lead to incorrect tax reporting in actual invoice copy and in SAP reports. Thus, get the tax code, tax amount, and tax base amount from legacy systems and map to SAP fields.

Check all the standard tax reports and your custom reports, all documents posted through interface should appear in all reports with correct tax base amounts, tax amounts, and tax codes.

Customer and Vendor:

You need to get the customer and vendor for documents to post from the non- SAP system. You can have a different interface for master data or you can map the customer and vendor number to legacy systems based on your design of customers and vendors master data with a non- SAP system.

GL Accounts:

GL account determination is depending on the legacy system and business processes. If the non- SAP system chart of account is mapped to SAP chart of account then, SAP will receive GL accounts from non- SAP system directly, but if there is no chart of accounts mapping in both systems then you need to create GL account determination tables in SAP or Legacy system based on business requirements, like VKOA table in SAP.

Dependent Fields:

Some fields in AR and AP documents have a dependency on the business processes, which need to identify and get the correct data into those fields. Below are some examples

  • The customer invoice number is mandatory in tax reports so if the legacy system in generating invoice number then it should be stored in the correct field like a reference, which is used in SAP standard tax reports. Also, check your customized reports where the customer invoice number is used.

  • Assignment field is primarily used in clearing transactions so map it with the correct field and fill the correct data to clear the incoming payments, or any other manual or auto clearing.

  • Your Customer statements or periodic statements which SAP sends to customer or vendors should have the invoice number, check what fields on statements are appearing for the invoice number and ensure this field data is getting into SAP from the interface.

  • Identify other fields which are required for the business and to execute the other business processes considering your customized reports and transaction codes.

Controlling Data:

Check your business process requirements for controlling data like a profit center, cost center, COPA, etc. If the legacy system is not providing the controlling data then design the table based on the business requirement to determine the cost and profit center. Ensure all the CO documents are generating as per the business processes and all the reports are correct in controlling.

Customs Fields:

Some field data from legacy systems which may require to store in SAP documents for business requirement.  To map this data, create custom fields in table ACODCA (In S4 HANA) or BSEG. You also can use standard fields which are not used in your documents like reference key 1, 2, and 3.

Document types:            

Based on business requirements create new document types or use the same standard document types as KR, KG, and DR, DG. Prefer to create new document types because it is always easy to identify the documents from the interface and can be traced easily if there are any issues.  Also, if the business needs any report in the future then they can easily be extracted by filtering on document types or building a custom report.

Reversal Transaction:

You need to consider the process of reversing the document in the legacy system. If you are reversing the document in a non-SAP system and then you are posting the same reversal document in SAP through the interface then you have to clear it manually in SAP with the original document, or you can schedule a job to clear reversal documents in SAP.


While designing a new interface many fields need to be taken care of. Always check the mandatory fields, business requirements, and the dependent fields to build the interface. Also, understand the FI document posting process in the Non-SAP system to understand each field.
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