No internal address no. exists for external address no. &1 (partner &2)

What causes this issue?

You have tried to determine an internal address number for the external
address number &V1& (Partner &V2&) of the direct input interface. There
is no external address number for this internal address in the system.

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?

Check the data that entered the system via the direct input interface.

Error message extract from SAP system. Copyright SAP SE.