Entry in inbound table already exists

What causes this issue?

Inbound parameters already exist in the partner profile under the
following key:
&v1&
This relates to the key fields in table EDP21:
SNDPRN Partner number
SNDPRT Partner type
SNDPFC Partner function
MESTYP Message type
MESCOD Message code
MESFCT Message function
TEST Test indicator

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?

Please check the EDI partner profile.
IF &DEVICE&='SCREEN'
<DS:TRAN.WE20>Execute function</>
ENDIF

Error message extract from SAP system. Copyright SAP SE.