No valid self-billing display type key in IDoc

What causes this issue?

An incorrect value for determining the credit memo type was transferred
in the IDoc in the segment/field E1EDKo1/ACTION.

System Response

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

How to fix this error?

You can enter a valid value with the function <Change data>. The
following values are currently supported:
005 Normal credit memo display
006 Clearing invoice (after retroactive price change)
007 Non-valued goods receipt
For reasons of compatibility, values 000 (same meaning as 005), and 001
(same meaning as 006) are supported. However, you should only use those
values listed above, that is 005, 006 or 007.
For value 007, the system assumes that data transferred is for
information purposes only. The data record is deactivated as far as the
program is concerned. Processing in the processing step is completed. A
manual change of the deactivtaion is not possible.

Error message extract from SAP system. Copyright SAP SE.