Call of function module for blocking/unblocking in RAR system failed

What causes this issue?

You tried to block or unblock a customer integrated with the Revenue
Accounting and Reporting (RAR) system. The call of the function module
for blocking or unblocking data in RAR failed.

System Response

System cannot block or unblock customers in RAR.

How to fix this error?

Contact your system administrator.

Procedure for System Administrators

To solve the problem, adhere to the following steps:
If the error occurred during blocking of data, verify that function
module <AB>FARR_DPP_BLOCK_CUST </>is available in your RAR system. If it
isn't, implement SAP Note 2765017.
If the error occurred during unblocking of data, verify that function
module <AB>FARR_DPP_UNBLOCK_CUST </>is available in your RAR system. If
it isn't, implement SAP Note 2765017.
If the function modules are available in your RAR system, verify that
the connection with the RAR system is working properly.

Error message extract from SAP system. Copyright SAP SE.