&1 is not in customer namespace

What causes this issue?

You want to create a new key figure. The key of this new key figure (
&V1&) is not in the customer namespace.

System Response

Processing terminated.

How to fix this error?

You have to create a customer-defined key figure starting with <LB>YY
</>... or <LB>ZZ</>....

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.