Specify a processor ID

What causes this issue?

If parked accounting documents are generated with Workflow from the
transaction data of the payment card file, then an agent group must be
determined for the processing of the documents in Workflow.
An agent group also has to be specified, if in a single case neither
parked documents or documents are generated with Workflow.

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

System Response

How to fix this error?

Error message extract from SAP system. Copyright SAP SE.