Posting occurs with many different types of documents.  It indicates that all sides of the FI entry are in balance.  Posting actually writes the document to the G/L. 

Payment on the other hand is the actual issuing of a check.  Payments can also be processed in accounts receivable. 

In that case, you are posting (updating your books to reflect) the receipt of a check from a customer and the deposit of said check in the bank.

Accounts payable is processing the money your company owes to a vendor for goods and services received.  Account Payable is a liability on the balance sheet. 

Accounts receivable is collecting the money that other companies/customers owe you.  It is an asset on the balance sheet.

SAP is integrated.  In most instances, there isn't a "link."  The transaction directly updates the tables involved.  There is a semi-severance between FI/Payment to allow checks to be issued even if there's a minor imbalance in the FI side of the posting. 

Asset depreciation and physical inventory are some example that don't update FI (CO/FM) as soon as the document is saved.

Modules that appear in more than one place is caused by SAP trying to be flexible in where it places things on its menu, so that different users/companies find it easy to locate a given transaction within the confines of the module they work in.  This has become more pronounced since the change to role based authorization management.  That's why you can reach Create a 
requisition from 4 different pathways, why Project Systems is in both Logistics and FI, and why Travel Management is in both HR and FI. 

In some organizations, travel authorization and tracking is an HR function, in some it is an FI function.

Difference between Clear and Payments

Apart from processing open items, what is the difference between:
1. Accounting-->FA-->AR-->Document entry-->Incoming payment > F-28 and 
2. Accounting-->FA-->AR-->Account-->Clear F-32 and the difference between F-53 and F-44 in AP.

When you post a transaction, you will get a Accounting document. If you are creating a payment document through F-53 or F-58 without linking the Accounting document, than we have to create a link between the accounting document and payment document and that can be done through F-32 (for GL) and F-44 (for AP). An good example is when we make down payment, a payment document is created. If we post the invoice, an accounting document is created. To clear this payment document and accounting document, F-44 is used.

- F-28 will be used to make trasactions for income payments.
  Eg: If you receive from a customer by using above T code will be passed necessary entries.
- F-32 will used used for clear the Customer line items.
- F-53 will be used for making payments to vendors.
- F-44 will be used for clearing the Vendor Line items.

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