No action is defined in this list for function code '&1'

What causes this issue?

No action is defined in the list for the function code '&V1&', which
you have just initiated.
The problem is due to incomplete Customizing.

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?

Correct the Customizing settings, or contact your system administrator.

Error message extract from SAP system. Copyright SAP SE.