Customizing: Variable &1 not used in server

What causes this issue?

A variable that does not exist has been maintained.

System Response

The entry is ignored.

How to fix this error?

Check the spelling of this entry or delete the variable definition in
Customizing.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.