T51P6 setting &1 for non-retro (ARRS) not supported

What causes this issue?

Table T51P6 controls how international ARRRS/DDNTK processing should be
performed for a specific employer's cost.
The setting you have chosen is one of the following and is supported by
the international ARRRS/DDNTK processing, but not by XDEC.
4,,Garnishment, not a reduction
7,,Loan, no reduction
8,,Deduct garnishment, what is possible
9,,Deduct garnishment, what is possible, rest in arrears
A,,Employer advance for mandatory deductions
B,,Employer advance repaid, next period
G,,Garnishment, write rest to DDNTK and process next period

System Response

No ARRRS/DDNTK processing will be performed by XDEC.

How to fix this error?

Raise a Development Request that the setting should be supported by the
XDEC solution.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.