Vendor Aging Reports in SAP

Transaction Code -
1- S_ALR_87012078

Profitability Segment in MB1A

Transaction Code - OMBW
You can change the screen layout change for the movement type by using this transaction.

Open Document is not visible in F-53

Go to F110 and Check whether the Open Items of this Vendor are Blocked in any Proposal.
If it is so, Delete that Proposal and try making Manual Payment using F-53.

Stock Ageing Report

1- Enter the material number and plant in table MCHB.
2- Get the batch number from above step where unrestricted stock is not equal to zero and sort the enteries in ascending order of their created date.
3- Enter the material number, plant, movement type (101), batch number from above step in the table MSEG to get the material document number.
4- Select the last recent record by batch number from step 3. Delete the other records.
5- Calculate the date difference. Formula (Current Date - Material Document Posting Date).

FI and MM Integration

1- OMBA- This transaction is used for MIGO and FI Document Type configuration.
2- OMWB - This transaction will show the simulation of Material movement and FI GL Account Posting.
Check OMWD
OMSK - VGA with Account category link & Material type with Account category reference link as well
OBYC - for BSX Transaction event key check which GL assigned against your valuation class.

https://blogs.sap.com/2014/05/07/mm-fi-integration-a-conceptual-understanding/

https://blogs.sap.com/2014/05/20/mm-fi-integration-account-determination-simulator/

Previous Month Date and Get the Start and End Date

"PASSING PREVIOUS MONTH DATE AND GET THE START AND END DATE"
CALL FUNCTION 'HR_JP_MONTH_BEGIN_END_DATE'
  EXPORTING
    IV_DATE                  = V_DATE
 IMPORTING
   EV_MONTH_BEGIN_DATE       = V_START_DATE
   EV_MONTH_END_DATE         = V_END_DATE.
"END OF PASSING PREVIOUS MONTH DATE AND GET THE START AND END DATE"

Identify the follow on documents from a given document

https://blogs.sap.com/2013/04/03/identify-the-follow-on-documents-from-a-given-document/