The search field ID '&3' is unknown

What causes this issue?

If the business partner group of a caller is to be determined in
routing, for example, the business partner ID of the caller has to be
identified first. Search tables, in which telephone numbers and e-mail
addresses are assigned to the business partner IDs, for example, are
used for this purpose. The search field ID describes which type of
information is used for identification, for example the telephone
number or e-mail address.
The search table specified here contains the assignment of '&V3&' to '
&V4&'. The seach field ID '&V3&' is not known to the routing server.
The server concerned is '&V1&'.
Further information:
Message from external software component: &V2&
<DS:REPO.RSRTRCDSP>BCOM Rule-Based Routing Trace</>

System Response

The function was not executed.

How to fix this error?

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

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.