Different trading partners & and & in payment document

What causes this issue?

In the standard system, only one trading partner may be stated in an
accounting document. The unambiguity per document is needed for
consolidation.

System Response

The payment document cannot be posted.

How to fix this error?

Payment transactions can generally be ignored for consolidation. It is
therefore possible to specify for a document type that the trading
partner does not have to be unique.

Error message extract from SAP system. Copyright SAP SE.