Error in update type from BAdI implementation

What causes this issue?

You have implemented the BAdI TPM_TAX_CALCULATION to change tax flows.
However, the implementation returned an incorrect update type for the ID
number. You need to enter an update type other than the one for the
outgoing flow.

System Response

The system terminates the cash flow calculation.

How to fix this error?

Correct the BAdI implementation.

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.