Documents exist referencing & and date & for invoicing party &

What causes this issue?

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

System Response

The system refers you to a possible double entry of the same invoice
document, and thus a possible double payment.

How to fix this error?

The current document can be posted despite this message. If you want to
avoid a possible double entry:
Check whether the current document has already been entered in the
system.
If necessary, check that your entry (reference number) is correct.

Error message extract from SAP system. Copyright SAP SE.