Wrong document type was selected for processing.

What causes this issue?

The program has tried to process a reversal for a 'child' document,
where its header document has not yet been reversed.

System Response

The system has stopped processing the reversal of the document. No
documents have been created.

How to fix this error?

Contact your system administrator

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.