In SAP Contract Accounts Receivable and Payable (FI-CA), which manages receivables for SAP BRIM, clearing rules are configured using clearing control. This control is defined by clearing variants, which specify how incoming payments are matched against open receivables. The main transaction and sub-transaction are fundamental attributes of an FI-CA document that classify the business transaction. By assigning different main/sub-transactions to receivables originating from different products, you can configure a clearing variant to specifically group and sort these items, thereby prioritizing them during the clearing process. This is the standard mechanism for implementing differentiated clearing logic based on the nature of the receivable.

A. Cost center: This is a Controlling (CO) object used for internal cost management and reporting; it does not influence external customer payment clearing rules in FI-CA.

B. Product: The product is the basis for the rule, but the rule itself is not defined within the product master data. The product information is used to derive the main/sub-transaction.

C. General ledger account: This is a Financial Accounting (FI) object for posting and reporting. While FI-CA items post to G/L reconciliation accounts, the account itself does not define clearing logic.

1. SAP S/4HANA - Official Vendor Documentation: In the section on Clearing Control, the system for defining clearing rules is detailed. It states, "You define the rules for clearing in a clearing variant... For each clearing step, you can define rules for grouping and sorting the items." The available fields for sorting and grouping explicitly include Main Transaction (VTREF) and Subtransaction (VTRE2).

Source: SAP Help Portal, SAP S/4HANA, Contract Accounts Receivable and Payable (FI-CA) -> Clearing -> Clearing Control -> Clearing Variant.

2. SAP S/4HANA - Official Vendor Documentation: The documentation on business transactions explains the role of main and sub-transactions. "Every posting in Contract Accounts Receivable and Payable is based on a transaction... The main and sub-transactions are the key for controlling business transactions." This control extends to dunning, interest calculation, and clearing.

Source: SAP Help Portal, SAP S/4HANA, Contract Accounts Receivable and Payable (FI-CA) -> Basic Functions -> Postings and Documents -> Basic Settings -> Main and Subtransactions.